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#	docs/rfc/README.md
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Tianyi Cui
2026-07-04 02:15:52 +08:00
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@@ -80,6 +80,7 @@ Do NOT write one for a mechanical or local choice (a variable name, a one-file r
| Title | First proposed |
|---|---|
| [Filesystem tool schemas — model-facing read/write/edit shapes](implemented/feature/2026-06-17-filesystem-tool-schemas.md) | 2026-06-17 |
| [Rich ACP bash rendering — the terminal card (`_meta`) and command classification](implemented/feature/2026-06-18-acp-terminal-and-tool-rendering.md) | 2026-06-18 |
| [Compaction as a capability seam (abstract contract + basic backend)](implemented/feature/2026-06-18-compaction-capability-seam.md) | 2026-06-18 |
| [Subagent capability seam](implemented/feature/2026-06-21-subagent-capability-seam.md) | 2026-06-21 |
@@ -97,6 +98,7 @@ Do NOT write one for a mechanical or local choice (a variable name, a one-file r
| [Keep one public stop primitive](implemented/simplification/2026-06-20-public-agent-stop-surface.md) | 2026-06-20 |
| [Fold trace-only session facts into load-bearing events](implemented/simplification/2026-06-20-collapse-trace-only-session-events.md) | 2026-06-20 |
| [Stop mirroring durable boundaries as agent events](implemented/simplification/2026-06-20-remove-agent-boundary-mirror-events.md) | 2026-06-20 |
| [Split the filesystem seam — provider text mutations plus the `dsh-fs-policy` plugin](implemented/simplification/2026-06-26-fsspec-style-fs-seam.md) | 2026-06-26 |
### Architecture
@@ -114,13 +116,20 @@ Do NOT write one for a mechanical or local choice (a variable name, a one-file r
| [Two LLM adapters as a design-verification twin](implemented/architecture/2026-06-13-twin-llm-adapters.md) | 2026-06-13 |
| [Session persistence as an abstract service over `SessionEvent`](implemented/architecture/2026-06-14-session-persistence.md) | 2026-06-14 |
| [Every session event is enclosed in a turn](implemented/architecture/2026-06-15-turn-enclosure-invariant.md) | 2026-06-15 |
| [Filesystem capability seam — ctx.fs, local backend, and model-facing filesystem tools](implemented/architecture/2026-06-17-filesystem-capability-seam.md) | 2026-06-17 |
| [Shared persistence write coordinator](implemented/architecture/2026-06-18-shared-persistence-write-coordinator.md) | 2026-06-18 |
| [Agent lifecycle and ownership seams](implemented/architecture/2026-06-18-agent-lifecycle-and-ownership-seams.md) | 2026-06-18 |
| [Session surface — a linked list over the event log for LLM message derivation](implemented/architecture/2026-06-18-session-surface.md) | 2026-06-18 |
| [Reorganize packages into a modular hierarchy](implemented/architecture/2026-06-20-package-hierarchy.md) | 2026-06-20 |
| [Branded IDs everywhere they belong](implemented/architecture/2026-06-20-branded-ids.md) | 2026-06-20 |
| [Extract example apps into packages](implemented/architecture/2026-06-20-extract-example-app-packages.md) | 2026-06-20 |
| [Web capability seam — provider registry and model-facing web tools](implemented/architecture/2026-06-24-web-capability-seam.md) | 2026-06-24 |
| [Make `dsh-fs-policy` an event-gate plugin, not a method interface](implemented/architecture/2026-06-26-file-context-as-event-gate.md) | 2026-06-26 |
| [Event-domain semantics — session is the fact log, agent is the live surface](implemented/architecture/2026-06-30-event-domain-semantics.md) | 2026-06-30 |
| [Resolve filesystem paths against the caller's session cwd](implemented/architecture/2026-07-02-fs-per-session-cwd.md) | 2026-07-02 |
| [Tagged render-intent union for tool-call presentation](implemented/architecture/2026-07-02-tool-render-intent-union.md) | 2026-07-02 |
| [Result-time applied-hunk diffs for file mutations](implemented/architecture/2026-07-02-result-time-applied-hunk-diffs.md) | 2026-07-02 |
| [Add direct directory listing to the filesystem seam](implemented/architecture/2026-07-03-filesystem-directory-listing-seam.md) | 2026-07-03 |
### Process
@@ -136,6 +145,8 @@ Do NOT write one for a mechanical or local choice (a variable name, a one-file r
| [Core-data-structures catalog and the `ts type-equiv` drift gate](implemented/process/2026-06-20-core-data-structures-catalog.md) | 2026-06-20 |
| [Generated cordis events + services catalog](implemented/process/2026-06-20-generated-cordis-catalog.md) | 2026-06-20 |
| [Classify RFCs by kind via path-encoded subdirectories](implemented/process/2026-06-20-rfc-classification.md) | 2026-06-20 |
| [Generated tool-schema catalog (boot-and-harvest)](implemented/process/2026-07-02-tool-schema-catalog.md) | 2026-07-02 |
| [Bilingual documentation via paired sibling files and a pairing gate](implemented/process/2026-07-02-bilingual-docs-and-pairing-gate.md) | 2026-07-02 |
### Testing

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@@ -10,6 +10,6 @@ Update it **in place** to state the current truth. Do **not** leave the outdated
### This is not a license to rewrite the *decision*
Keeping the shipped-state description current is about **facts** (paths, names, structure, defaults) — not about silently flipping the **decision and its rationale** into a different one. If the underlying choice itself is reversed or materially changed (not just relocated), that is a new decision: write a new RFC and cross-link, per [rfc/README.md](../README.md) ("An RFC is never edited into a different decision"). The line: a refactor that moves where the decision is *realized* → edit this RFC to match; a reversal of *what was decided* → a new RFC.
Keeping the shipped-state description current is about **facts** (paths, names, structure, defaults) — not about silently flipping the **decision and its rationale** into a different one. The "new RFC" escape hatch is for **macro** changes — a genuine reversal of *what was decided* or its rationale — NOT for renames, moves, or structural relocations. A rename is always a fact to fix **in place**: leaving a package/symbol/path at its old name (even with a "was renamed to…" aside) only confuses a reader who greps the current tree for a name that no longer exists. So: the package was renamed, a symbol changed, a plugin moved, the decision is now realized through a different mechanism → edit this RFC to state the current names and structure. Only a reversal of *what was decided* → a new RFC and cross-link, per [rfc/README.md](../README.md) ("An RFC is never edited into a different decision").
When in doubt, ask whether a reader following this RFC to the code would land on something real. If not, it needs updating.

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# RFC: Filesystem capability seam — ctx.fs, local backend, and model-facing filesystem tools
Status: implemented
## Problem
The harness has a concrete `bash` capability seam (`dsh-bash` / `dsh-bash-local` / `dsh-tool-bash`), but filesystem operations are about to be added as model-facing tools without an equivalent seam. If `read`, `write`, and `edit` directly use `node:fs`, the model-facing tool package will own filesystem execution policy, local path resolution, atomic write behavior, text decoding, symlink behavior, and edit semantics all at once.
That couples three concerns that change independently:
1. The filesystem contract: what operations plugins can ask for.
2. The backend: local disk now, sandboxed/remote/project-scoped filesystem later.
3. The consumer surface: model-facing `read` / `write` / `edit` schemas and result formatting.
Without a `ctx.fs` interface, swapping local filesystem access for a sandboxed or remote backend would churn the tool schemas, demos, and prompt guidance even when the model-facing contract should stay stable. It also makes permission/sandbox boundaries harder to reason about: a `cwd` option can look like a sandbox even though it is only a base path unless an explicit backend or `tools/execute` policy enforces containment.
We need the filesystem tools to land in the same capability-seam shape as bash before they become a public package surface.
## Proposal
Introduce filesystem access as a first-class capability seam following [the capability-seam RFC](../../implemented/architecture/2026-06-13-capability-seams.md):
1. `@deepseek-ai/dsh-fs` (`packages/fs/fs`) owns the abstract `ctx.fs` service, the filesystem vocabulary types, and the `fs/*` policy event vocabulary.
2. `@deepseek-ai/dsh-fs-local` (`packages/fs/fs-local`) provides the first implementation, backed by the local filesystem.
3. `@deepseek-ai/dsh-tool-fs` (`packages/fs/tool-fs`) provides the model-facing `read`, `write`, and `edit` tools over `ctx.fs`, and is the executor that dispatches the `fs/*` events.
The consumer package depends only on the interface package, never on `dsh-fs-local`. A deployment that wants a different backend loads a different provider for `ctx.fs` without changing the tool schemas or model-facing prompt guidance.
The read-before-write/edit and observed-state policy is a fourth package, `@deepseek-ai/dsh-fs-policy` (`packages/fs/fs-policy`), contributed through the `fs/*` event gate rather than living on `ctx.fs`. This RFC established the three-package seam; the split of policy off the provider base class is decided by [the split-fs-seam RFC](../simplification/2026-06-26-fsspec-style-fs-seam.md), and its realization as an event-gate plugin (not a method service) by [the event-gate RFC](2026-06-26-file-context-as-event-gate.md). This document is updated to describe that landed four-package shape.
The first backend is deliberately local-only: `dsh-fs-local` implements `ctx.fs` against the host filesystem. Future sibling backends can provide sandboxed, remote, virtual, or project-scoped filesystems behind the same interface.
The first consumer is deliberately text-file-only: `dsh-tool-fs` exposes model-facing `read`, `write`, and `edit` tools for UTF-8 text files. Future consumers can add directory listing, search/glob, binary-safe operations, file watching, or higher-level project operations without changing the local backend package, as long as the needed capability exists on `ctx.fs`. Direct directory listing was later added by [Add direct directory listing to the filesystem seam](2026-07-03-filesystem-directory-listing-seam.md).
Filesystem permissions and sandboxing are not implied by this split. The local backend resolves relative paths from its configured base directory, but containment policy is a separate decision: either a stricter `ctx.fs` implementation enforces it, or a permission/sandbox plugin wraps `tools/execute` and vetoes calls before they reach the consumer.
Read-before-write/edit and observed-state are policy, contributed by the `dsh-fs-policy` plugin through the `fs/*` event gate — NOT stored on `ctx.fs`. The provider seam offers an optional version guard on its mutations (`writeText`/`editText` take an optional expectation); the policy plugin decides that guard by listening on `fs/write-intent`/`fs/edit-intent` and records observed versions on `fs/observed`. The executor (`dsh-tool-fs`) passes the current tool execution context as the opaque event actor; the policy plugin derives the observed-state owner from it, normally `exec.agent.session`. `dsh-fs` treats the actor as opaque and never reads it; `dsh-tool-fs` never reaches into the policy plugin. Authorization is version freshness: any read records the file's version, and a later write/edit is authorized as long as the file is unchanged. (This RFC first placed the observed-state store on `ctx.fs`; the split to `dsh-fs-policy` on the `fs/*` event gate is decided by [the split-fs-seam](../simplification/2026-06-26-fsspec-style-fs-seam.md) and [event-gate](2026-06-26-file-context-as-event-gate.md) RFCs.)
## Package topology
The filesystem seam uses the same dependency direction as the bash trio:
```text
@deepseek-ai/dsh-tool-fs --depends on--> @deepseek-ai/dsh-fs <--depends on-- @deepseek-ai/dsh-fs-local
consumer interface implementation
```
`@deepseek-ai/dsh-fs` depends only on `cordis` plus the repo-wide `HarnessError` base from `@deepseek-ai/dsh-llm`. It declares the `ctx.fs` key, the abstract `FileSystem` service, the vocabulary types shared by backends and consumers, the filesystem error vocabulary, and the `fs/*` policy event vocabulary. It carries no observed-state store and no owner-derivation shape; the events pass an opaque `object` actor that the provider never reads, and the `dsh-fs-policy` plugin owns the owner-derivation shape and the observed-state store on top of those events.
`@deepseek-ai/dsh-fs-local` depends on `@deepseek-ai/dsh-fs` and `cordis`. It subclasses `FileSystem`, registers itself as `ctx.fs`, owns local-backend configuration such as the base directory, and contains all direct `node:fs` / `node:path` access. It holds no observed-state store — freshness is a version token the backend mints and the policy plugin records.
`@deepseek-ai/dsh-tool-fs` depends on `@deepseek-ai/dsh-fs`, `@deepseek-ai/dsh-tools`, `@deepseek-ai/dsh-system-prompt`, and `cordis`. It registers model-facing tools and prompt sections. It must not import `node:fs`, `node:path`, or `@deepseek-ai/dsh-fs-local`; filesystem execution always goes through `ctx.fs`. If the implementation needs concrete agent or session helper types, those dependencies belong in `tool-fs`; they must not leak back into `dsh-fs`.
The root `tool-fs` plugin registers the full filesystem tool suite (`read`, `write`, and `edit`) by composing the per-tool registration helpers. It injects `fs` and never imports an implementation package.
## `ctx.fs` contract
`@deepseek-ai/dsh-fs` owns a semantic filesystem service. It is higher-level than `readFile` / `writeFile` so `tool-fs` does not reimplement path resolution, versioning, text decoding, binary rejection, pagination, atomic replacement, symlink behavior, or literal edit semantics.
The exact TypeScript signatures are implementation details for the PR, but the interface must cover four semantic operations:
- Resolve a model/plugin-supplied path into a backend-defined target.
- Stat target metadata without reading file contents.
- Read a bounded UTF-8 text page from a target.
- Create or replace a UTF-8 text file.
- Edit an existing UTF-8 text file by literal replacement.
The provider seam also carries the freshness hooks that policy builds on — but the observed-state store and owner derivation live in the `dsh-fs-policy` plugin, not on `ctx.fs`:
- The backend mints an opaque `version` token per target (in `stat` and in every read/mutation outcome).
- `writeText`/`editText` take an OPTIONAL version expectation: omit it for an unconditional bare-provider mutation, or supply it to guard the mutation inside the backend's atomic critical section.
- The `dsh-fs-policy` plugin decides that expectation on `fs/write-intent`/`fs/edit-intent` and records observed versions on `fs/observed`, keyed by an owner it derives from the opaque event actor (normally `exec.agent.session`).
Authorization is version freshness, not a full/partial view distinction: any read records the target's version, and a later write/edit is authorized as long as the file is still at that version — so a windowed read of lines 100-150 authorizes an edit of line 120. The observed-state store is a `WeakMap<owner, Map<targetKey, version>>` inside `dsh-fs-policy`; `dsh-fs` holds none of it and treats the actor as opaque. (This RFC first modeled a `FileState` cache with `full`/`partial` views on `ctx.fs`; the split-fs-seam and event-gate RFCs replaced that with the freshness-based policy plugin described here.)
Path resolution should be explicit and allowed to be async. Local resolution may only normalize a path, but sandboxed/remote/project-scoped backends may need I/O to resolve a user-supplied path into a stable target identity.
Resolved targets must expose at least three concepts:
- The original input path, for diagnostics.
- An opaque `targetKey`, used for stale guards and file-state lookup. The local backend might use a realpath-like key; a remote backend might use a workspace URI or file id. Consumers must not parse or assume this is a local absolute path.
- A `displayPath`, used for model/UI-facing output. It may be a local absolute path, workspace-relative path, or remote URI depending on the backend.
Read and mutation results must include an opaque file `version`. A local backend can use mtime/size or a hash-like token; a remote backend can use a revision id. `ctx.fs` records versions in its file-state store for stale checks; consumers may display related metadata but must not interpret the version token.
The provider hands back decoded text: `readText` returns a whole regular text file, `streamText` streams the same text semantics for large files. Both own regular-file checks, bounded line/output handling is NOT theirs — line windowing, numbered-line rendering, and total-line accounting live in the executor (`dsh-tool-fs`), which reads through `ctx.fs` and renders the model-facing window. The provider owns UTF-8 decoding and binary/NUL rejection; it does not know about line windows or views.
Observed-state recording is not on `ctx.fs`: after a successful read the executor emits `fs/observed`, and the `dsh-fs-policy` plugin records `{ version }` for the deriving owner. There is no `full`/`partial` view — a read at any window records the version, and freshness (not view completeness) authorizes a later write/edit.
Full-file writes create or replace UTF-8 text files. Backends may create parent directories when that behavior is supported and documented. Existing non-regular targets are rejected. `writeText` takes an optional expectation: `createIfAbsent` creates a missing target and rejects an existing one with `FS_NOT_OBSERVED` (the path the policy uses for an unobserved owner); `replaceIfVersion` replaces only when the target exists at the observed version, else `FS_STALE_VERSION`; omitting the expectation is the unconditional bare-provider create-or-overwrite. The policy plugin chooses which expectation to supply from the owner's observed state.
Literal edit is a provider primitive (`editText`), not composed in `tool-fs` from a read plus write. Literal matching, duplicate-match rejection, CRLF preservation, binary rejection, optional stale-version checking, and atomic read-modify-write must stay together inside the backend's mutation critical section. `editText` takes the same optional version expectation; the stale check runs before literal matching so an edit against an old read reports `FS_STALE_VERSION`. A remote backend may implement edit as a native compare-and-edit operation; the consumer should not force local-style composition.
The policy plugin, not `ctx.fs`, gates on prior observation: an `edit` requires a prior observation by the owner (else `FS_NOT_OBSERVED`), and the recorded version is passed to `editText` as the CAS basis. With the policy plugin absent, `ctx.fs` alone is a complete unconstrained seam (unconditional write/edit); the tool is never method-coupled to the policy.
Filesystem contract failures are thrown as `FsError extends HarnessError`, and the tool registry converts them into `isError` tool results with structured `{ name, code }` metadata. `dsh-fs` owns this vocabulary rather than each tool inventing messages. The codes are `FS_NOT_FOUND`, `FS_NOT_TEXT`, `FS_STALE_VERSION`, `FS_NOT_OBSERVED`, `FS_NOT_REGULAR_FILE`, `FS_AMBIGUOUS_EDIT`, `FS_EDIT_NOT_FOUND`, and `FS_ABORTED`. (An earlier draft included `FS_PARTIAL_OBSERVATION`; freshness-based authorization has no partial/full distinction, so it was dropped. Directory-listing-specific codes were added later by [Add direct directory listing to the filesystem seam](2026-07-03-filesystem-directory-listing-seam.md).)
## Tool consumer behavior
`@deepseek-ai/dsh-tool-fs` is the model-facing consumer. It owns tool names, JSON schemas, argument validation at the model boundary, prompt sections, and result formatting. It does not own filesystem execution.
The first tool suite contains:
- `read`: inspect a UTF-8 text file and return line-numbered content with pagination guidance.
- `write`: create or fully replace a UTF-8 text file.
- `edit`: update an existing UTF-8 text file by replacing literal text, requiring a unique match by default and allowing an explicit replace-all mode.
Each tool follows the same execution shape:
1. Validate and normalize model arguments.
2. Call the appropriate `ctx.fs` operation.
3. Format the result as `ContentBlock[]` for the model.
4. Let thrown backend/tool errors flow through `ToolRegistry.execute()`, which converts them into `isError` tool results.
The package registers prompt guidance through `ctx.systemPrompt.section(...)` and registers schemas through `ctx.tools.register(...)`. Tool schemas still flow into the normal prompt assembly path via `SystemPrompt.assemble()` and `ToolRegistry.schemas()`; no agent-loop changes are required.
The tool package must keep model-facing contracts stable when backends change. A local backend and a remote backend may resolve paths differently internally, but the `read` / `write` / `edit` schemas should not change solely because the backend changes.
The default deployment requires a prior `read` before updating an existing file with `write` or `edit`. `tool-fs` does not implement this by checking whether a tool named `read` ran: it dispatches the `fs/write-intent`/`fs/edit-intent` events (passing the execution context as the opaque actor), and the `dsh-fs-policy` plugin derives the owner, gates on prior observation, and supplies the version expectation. Any windowed read authorizes a later write/edit as long as the file is unchanged. Creating a new file with `write` does not require prior observation.
The root plugin registers the full suite by composing the per-tool registration helpers. It injects `fs`, `tools`, and `systemPrompt`.
## Migration plan
This RFC starts from `origin/master`, where no filesystem tool package exists yet. The landed implementation adds the new three-package topology directly:
1. Add `packages/fs/fs` with the `ctx.fs` abstract service and vocabulary types.
2. Add `packages/fs/fs-local` with the local backend implementation and backend-level tests.
3. Add `packages/fs/tool-fs` with the model-facing `read`, `write`, and `edit` tools over `ctx.fs`.
4. Update `docs/architecture.md`, `packages/README.md`, package READMEs, build/typecheck config, and aggregate maintenance scripts such as `scripts/publint-all.ts`.
This RFC's first landing kept the observed-state store behind `ctx.fs`. The split-fs-seam and event-gate RFCs then moved it into the standalone `@deepseek-ai/dsh-fs-policy` plugin on the `fs/*` event gate, which is the shipped shape; a deployment loading `dsh-tool-fs` also loads `dsh-fs-policy` to get read-before-write/edit.
Example leaf configs stay bash-only in this landing. Wiring `examples/coding-agent` or `examples/acp-agent` to `dsh-fs-local` + `dsh-tool-fs` changes the model prompt, visible tool schemas, and ACP snapshot transcript, so it should land as a follow-up UX/example change with prompt and snapshot updates in the same PR.
If this work is split into multiple PRs, they should follow the seam order:
1. Interface PR: `dsh-fs` only, with service registration and contract tests.
2. Implementation PR: `dsh-fs-local`, with real filesystem behavior tests.
3. Consumer PR: `dsh-tool-fs`, docs, and integration tests; example wiring follows in a separate prompt/snapshot PR.
The earlier combined package name `@deepseek-ai/dsh-fs-tools` should not become part of the new public surface.
## Tests
Tests should follow the package boundary, not only the user-visible tools.
`dsh-fs` tests cover the service seam itself: a provider registers `ctx.fs`, duplicate providers follow Cordis service behavior, disposal removes the service, and any shared contract helpers or type-level utilities behave as documented.
`dsh-fs-local` tests cover real filesystem behavior through the `ctx.fs` interface, not through model tools. They should include path resolution, absolute paths, `..` segments, symlinks inside and outside the configured base directory, reading small and large text files, streaming, binary-file rejection, invalid-UTF-8 rejection, abort handling, unconditional and version-guarded full-file writes, `createIfAbsent`/`replaceIfVersion` semantics, parent-directory creation, non-regular target rejection, literal edit success/failure, unique-match enforcement, replace-all behavior, line-ending preservation, stale-version rejection (guarded edit against an old version), and structured `FsError` codes. The observed-state/owner-derivation policy is NOT here — it lives in `dsh-fs-policy` and is tested there.
Beyond the happy/sad paths above, `dsh-fs-local` tests must cover the defensive-pattern classes this repo has been bitten by:
- **Atomic-write temp-file safety**, not just cleanup. The atomic replace must write its temp file into a private (`0700`) directory, with a random name and an exclusive owner-only (`'wx'`, `0o600`) open, mirroring the bash spill-file rules — predictable world-readable temp paths invite symlink races and disclosure. Assert the temp file's permissions and that a pre-existing temp path does not get clobbered, alongside the existing cleanup-on-failure path.
- **Implementation requirement:** `dsh-fs-local` write/edit use the same private-temp primitive: a random `0700` staging directory next to the target, an exclusive `0o600` temp file, cleanup on failure, and a final atomic rename. Do not move this RFC to `implemented/` if that primitive regresses or is deliberately revised.
- **`targetKey` identity through symlinks.** Two different input paths that resolve to the same realpath must share one file-state entry: a `read` via path A must satisfy the read-before-edit guard for an `edit` via symlink path B, and a stale write through one path must be detected through the other. This is the contract that makes the stale guard correct, so test it directly.
- **Concurrency / stale races.** The RFC names edit as race-prone (see Risks). Test that two concurrent write/edit operations against the same target settle deterministically: one succeeds and the other is rejected with `FS_STALE_VERSION` rather than silently overwriting, and that a successful edit refreshes recorded state so an immediately-following edit by the same owner proceeds.
- **HMR safety and disposal.** `dsh-fs-local` registers `ctx.fs` and owns the in-memory file-state store, so it needs its own HMR-safety test (register the backend on a fiber, dispose it, assert the `ctx.fs` provider is withdrawn and the file-state store is released — a later provider starts with no inherited state).
`dsh-tool-fs` tests cover the consumer surface against the real `dsh-fs-local` provider (mock only the model/clock, not the collaborator). They should verify tool schemas, argument validation, prompt-section registration, formatting of successful results, propagation of backend `FsError` codes into `isError` tool results through `ctx.tools.execute()`, that read/write/edit dispatch the `fs/*` events (passing the execution context as the actor), root-plugin suite registration, and HMR cleanup of both tool schemas and prompt sections.
Integration tests should load `dsh-fs-local` plus `dsh-tool-fs` (and, for the default deployment, `dsh-fs-policy`) and execute `read`, `write`, and `edit` through `ctx.tools.execute()` to prove the packages work together without bypassing the tool registry — including a bare-provider path (no `dsh-fs-policy`) where an unread edit/overwrite succeeds. They must verify the world, not the tool's self-report: after a `write`/`edit`, read the file back from disk and assert byte-identical content (and that untouched files are unchanged), rather than trusting the returned `ContentBlock[]`. Each integration/e2e test owns its resources — create the harness in the test, run against a per-test temporary directory, and dispose the harness and remove the directory in `afterEach` even on failure or timeout.
Repo gates for the implementation include the focused vitest suites, `pnpm run typecheck`, `pnpm run test:coverage` for runtime code, and build/publint coverage after adding package entrypoints.
## Risks
**`cwd` can be mistaken for a sandbox.** The local backend's base directory is a resolution default, not automatically a containment boundary. If containment is required, it must be enforced by the backend contract or by a permission/sandbox plugin on `tools/execute`.
**The interface can become too local.** Returning fields such as `absolutePath` from `ctx.fs` would make remote, sandboxed, or virtual backends awkward. The contract should expose display metadata without requiring consumers to understand host paths.
**The interface can become too thin.** If `ctx.fs` only mirrors `node:fs` primitives, `tool-fs` will reimplement binary detection, pagination, atomic writes, and edit semantics. That recreates the coupling this RFC is trying to avoid.
**Edit semantics are race-prone.** Literal edit is a read-modify-write operation. Without a stale-content guard or backend-level atomic edit primitive, concurrent edits can overwrite each other. The first implementation should document its guarantees clearly; stronger compare-and-swap semantics can be added later if needed.
**Observed state does not belong on `ctx.fs`.** Recording what an execution context has seen is workflow policy, not raw filesystem I/O. This RFC first placed it inside the filesystem seam; the split-fs-seam RFC then established that a sandboxed/remote backend should not inherit model-facing observation policy, and moved it into the `dsh-fs-policy` plugin. The provider seam keeps only what write/edit safety genuinely needs at the storage layer — a backend-minted version token and an optional version-guarded mutation — while the policy plugin owns owner derivation, observed-state, and read-before-edit gating over the `fs/*` events.
**The `resolve`-then-operate shape costs an extra round-trip per call.** Each tool may resolve a path to an `FsTarget` and then issue the read/write/edit as a separate `ctx.fs` call. For the local backend this is negligible (resolution is in-memory path normalization), but a remote/sandboxed backend may turn each step into its own request, so a single `read` can become two network round-trips. Backends where the round-trip matters can cache or fold resolution internally while preserving the observable contract.
**File-state persistence is deferred.** The first implementation can keep file state in memory. Resumed sessions should conservatively require files to be read again before write/edit tools accept updates until a future session-event or persistence mechanism makes file state replayable.
**Error codes become part of the seam.** `FsError` codes make stale-version and observation failures machine-routable through the existing structured error taxonomy. The cost is that `dsh-fs` imports the shared `HarnessError` base from `dsh-llm`; that dependency is intentional and should stay limited to the error vocabulary.
**Package churn is front-loaded.** The three-package split adds boilerplate before there is more than one backend. This is intentional: filesystem access is a likely sandbox/remote boundary, and changing the package surface after shipping model-facing tools would be more expensive.

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@@ -37,7 +37,7 @@ The old `base*.yml`/`acp-tail.yml` includes already deduped the *config*, but a
## Verification
- Each example directory is `cordis.yml` (+ the acp `cordis.snapshot.yml`) + `README.md` + tests only — no `start.ts`, no infra preamble; `base.yml`/`base-core.yml`/`acp-tail.yml` are gone.
- `demo:echo` / `demo:coding` / `demo:acp` run via the app-package `bin`s.
- `demo:echo` / `demo:repl` / `demo:acp` run via the app-package `bin`s.
- The new packages carry the per-file 100% coverage gate and a README like every `@deepseek-ai/dsh-*`. Each app package has a keyless **real-load-path** smoke that boots it through its `bin` + the cordis Loader (not a hand-built `ctx.plugin({...})` mount), guarding the `unwrapExports` export-shape bug class ([postmortem 0001](../../../postmortem/0001-acp-default-export-drops-inject.md)).
- The ACP snapshot **replay** transcript is unchanged: the boot restructuring preserved the plugin set + load order, so `pnpm run test:snapshot` stays green against the committed goldens with no re-record.

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# RFC: Web capability seam - stable tools over multiple providers
Status: implemented
## Problem
The harness needs model-facing web tools without binding the model contract to one vendor's API shape. Search is the immediate pressure point: the first version should support at least Exa search and Perplexity search — two deliberately different provider shapes (Exa returns a flat `results[]` of `{title, url, highlights, publishedDate}`; Perplexity returns a generated answer plus citations), which is what proves the normalized seam does not just mirror one vendor. Fetch is a separate capability: an anonymous public HTTP(S) fetch backend has transport, security, redirect, decoding, and size-limit concerns that are not the same as provider-backed search.
The model-facing surface should stay stable while backends change. A search provider swap should not change how the model asks for a query, and a fetch implementation swap should not change how the model asks for a URL. Conversely, a provider package should not expose its own model-facing tool schema just because it has extra provider-specific knobs.
Putting search and fetch directly in `dsh-tool-web` would make the model-facing tool own provider selection, backend request mapping, transport policy, result normalization, prompt guidance, presentation, and schema registration at once. Letting each provider register its own tool has the opposite problem: tool availability, names, descriptions, and parameters would depend on whichever provider packages happen to load, and provider-specific fields would leak into the model contract.
There is also a provider-selection question. Existing `tool-bash` and `tool-fs` can rely on Cordis `inject` because there is one backend service key. Web has two independent capabilities (`search` and `fetch`) and potentially multiple providers per capability. `inject: ['web']` proves the seam exists; it does not prove a usable search or fetch provider exists, and it does not define which provider should win when several are registered.
## Proposal
Introduce web access as a first-class capability seam following [the capability-seam RFC](../../implemented/architecture/2026-06-13-capability-seams.md):
1. `@deepseek-ai/dsh-web` (`packages/web/web`) owns `ctx.web`, provider registration, provider selection, shared request/result vocabulary, and web-specific errors.
2. Provider packages implement concrete backends and register capabilities with `ctx.web`, for example `@deepseek-ai/dsh-web-search-exa`, `@deepseek-ai/dsh-web-search-perplexity`, `@deepseek-ai/dsh-web-search-deepseek`, and `@deepseek-ai/dsh-web-fetch-local`.
3. `@deepseek-ai/dsh-tool-web` (`packages/web/tool-web`) owns the model-facing `web_search` and `web_fetch` tool schemas, prompt sections, argument validation, result formatting, and tool-owned presentation over `ctx.web`.
Providers do not register tools. Providers register capabilities. `dsh-tool-web` is the only owner of model-facing names, descriptions, prompt guidance, JSON schemas, and presentation.
Search and fetch are separate capabilities and separate model-facing tools, but they are deliberately one seam. `ctx.web` is a single web-access middle layer between provider packages on one side and the tool consumer on the other: one service to inject, one provider-selection policy owner, one abort/error vocabulary, one place a product configures "how this harness reaches the web." The two halves do not share a request schema and have no shared business logic — search normalizes provider-backed discovery into a portable result with optional answer text and citeable sources, while fetch retrieves a concrete public HTTP(S) URL and returns a status code plus bounded decoded content — but they are parallel registries on one capability surface, not two surfaces. The cost is a `WebService` whose registry/status/exec methods come in `Search`/`Fetch` pairs; that parallelism is intentional, not a missed extraction. Splitting into `dsh-search` and `dsh-fetch` is the rejected alternative below.
`dsh-tool-web` should register model-facing web tools when the product has enabled those tools and the `ctx.web` seam is present. Backend availability is an execution-time concern, not a schema-registration concern:
- Register `web_search` when web search is enabled for the product/app.
- Register `web_fetch` when web fetch is enabled for the product/app.
- Do not unregister a tool merely because its selected provider is missing, misconfigured, missing credentials, ambiguous, or temporarily unavailable.
- Resolve the provider at execution time, and return a structured `WebError` when the selected capability cannot run.
This keeps the model schema stable without making plugin load order, credential state, or HMR timing part of the model-facing contract. If web search is enabled but no usable search provider exists, `web_search` remains visible and execution fails with a structured `WebError` such as `WEB_PROVIDER_UNAVAILABLE` or `WEB_PROVIDER_CONFIGURED_UNAVAILABLE`. If a provider appears after `dsh-tool-web`, the next execution can use it without changing the schema. If a provider disappears mid-call, execution fails with a structured `WebError` instead of silently choosing another provider or falling through to `UNKNOWN_TOOL`.
The first version's provider-change signal is intentionally small. `web/providers-change` has no payload, carries no capability graph, and does not expose provider metadata. It means only "the provider registry changed; observers may recompute status from `ctx.web`." `searchStatus()` and `fetchStatus()` remain derived, not stored, and they are diagnostics plus execution-resolution inputs rather than tool-schema visibility switches.
## Package topology
The three-package interface/implementation/consumer split follows bash and filesystem, but the *interface* package is closer to the LLM seam. `LlmService` (`packages/llm/llm/src/index.ts`) is a name-keyed provider registry: `registerAdapter(models, adapter)` stores adapters in a `Map`, returns a disposer, throws `DUPLICATE_ADAPTER` on duplicate keys, and throws `NO_ADAPTER` at resolution time. `ctx.web` follows that registry shape, but has two capability kinds and one small selection-status layer so diagnostics and execution can explain why a search or fetch capability can or cannot run.
The dependency direction mirrors bash and filesystem:
```text
@deepseek-ai/dsh-tool-web --depends on--> @deepseek-ai/dsh-web <--depends on-- @deepseek-ai/dsh-web-search-exa
consumer interface implementation
<--depends on-- @deepseek-ai/dsh-web-search-perplexity
implementation
<--depends on-- @deepseek-ai/dsh-web-search-deepseek
implementation
<--depends on-- @deepseek-ai/dsh-web-fetch-local
implementation
```
At runtime, provider packages register capabilities with `ctx.web`; `tool-web` reads capability status and registers stable tools with `ctx.tools`:
```mermaid
flowchart LR
exa["@deepseek-ai/dsh-web-search-exa"] -->|registerSearchProvider| web["@deepseek-ai/dsh-web / ctx.web"]
perplexity["@deepseek-ai/dsh-web-search-perplexity"] -->|registerSearchProvider| web
deepseek["@deepseek-ai/dsh-web-search-deepseek"] -->|registerSearchProvider| web
fetchLocal["@deepseek-ai/dsh-web-fetch-local"] -->|registerFetchProvider| web
toolWeb["@deepseek-ai/dsh-tool-web"] -->|searchStatus/fetchStatus| web
toolWeb -->|ctx.tools.register| webSearch["tool: web_search"]
toolWeb -->|ctx.tools.register| webFetch["tool: web_fetch"]
```
`@deepseek-ai/dsh-web` depends only on Cordis and low-level harness support. It declares `ctx.web`, provider interfaces, request/result types, status types, and error codes. It does not import tool, agent, session, LLM, or provider packages.
Provider packages depend on `@deepseek-ai/dsh-web` and Cordis. They own credentials, endpoint config, provider-specific request mapping, provider-specific response parsing, and provider-specific error translation into `WebError`. They issue network requests with the platform-native `fetch` (Node 24), mirroring `@deepseek-ai/dsh-llm-deepseek`'s adapter, NOT a cordis HTTP-client service (`ctx.http`/`@cordisjs/plugin-http`) — even where a Perplexity provider's request is shaped like an OpenAI-compatible chat completion, that wire shape is a provider-private detail and does not make the provider depend on `ctx.llm`. A provider does NOT own the `ctx.web` key (two search providers cannot both own it): like `dsh-llm-deepseek`, each provider package is a function/namespace plugin (`inject: ['web']`) whose `apply` constructs the backend and calls `ctx.web.registerSearchProvider` / `registerFetchProvider`. `@deepseek-ai/dsh-web` is the `export default` service that owns the key.
`@deepseek-ai/dsh-tool-web` depends on `@deepseek-ai/dsh-web`, `@deepseek-ai/dsh-tools`, `@deepseek-ai/dsh-system-prompt`, and Cordis. It never imports concrete provider packages.
## `ctx.web` contract
`ctx.web` is a provider registry plus a provider-selecting execution surface. The registry half should stay close to `LlmService`: a `Map<id, provider>` per capability kind, `registerSearchProvider` / `registerFetchProvider` methods that return disposers, duplicate ids that throw `WebError`, and execution-time resolution that throws when the selected provider is absent or unusable. The exact TypeScript signatures belong to the implementation PR, but the seam should expose this shape:
```ts
interface WebSearchProvider {
readonly id: string
status(): WebProviderStatus
search(request: WebSearchRequest, exec?: WebExecContext): Promise<WebSearchResult>
}
interface WebFetchProvider {
readonly id: string
status(): WebProviderStatus
fetch(request: WebFetchRequest, exec?: WebExecContext): Promise<WebFetchResult>
}
interface WebService {
registerSearchProvider(provider: WebSearchProvider): () => void
registerFetchProvider(provider: WebFetchProvider): () => void
searchStatus(): WebCapabilityStatus
fetchStatus(): WebCapabilityStatus
search(request: WebSearchRequest, exec?: WebExecContext): Promise<WebSearchResult>
fetch(request: WebFetchRequest, exec?: WebExecContext): Promise<WebFetchResult>
}
interface WebExecContext {
readonly signal?: AbortSignal
}
```
`WebExecContext` is execution control, not business input. The first version should carry only `signal` so `tool-web` can propagate turn cancellation, tool timeout, and agent disposal into provider network requests, SSE readers, and expensive decoding. It should not pass `ToolExecution` through the seam, because that would make `dsh-web` depend on `dsh-tools`.
`@deepseek-ai/dsh-web` should also declare a Cordis event named `web/providers-change`. Provider ids are stable strings and unique within their capability kind. Registering a duplicate search provider id or duplicate fetch provider id should fail rather than silently replace the old provider. Provider registration returns a disposer, emits `web/providers-change` after successful registration, and emits it again when the provider is disposed. The registry should follow the existing `ctx.tools.register()` / `ctx.systemPrompt.section()` pattern: wrap the mutation in `ctx.effect()`, install the rollback disposer before emitting `web/providers-change`, and let a throwing registration-time change listener roll back the just-added provider instead of leaking it into the registry.
## Provider status and selection
Provider status and capability selection are separate concepts, but both stay minimal. A provider reports only whether that concrete implementation is usable by cheap local checks such as credential presence or parseable endpoint config. A provider `status()` must not make network calls. The service reports whether the capability has a selected usable provider, or why execution would fail.
`LlmService` has no status type at all: availability is expressed as registry membership plus a resolution-time throw. `ctx.web` needs a small status answer because product apps, diagnostics, tests, and execution can report precise provider-selection failures without probing individual providers from the tool layer. Status must be derived from the configured provider id, registered providers, and each provider's cheap local `status()` on each call; it must not be stored as mutable service state.
`WebCapabilityStatus` stays intentionally small: `available` plus a `reason` discriminant, and the selected `providerId` on the available branch so diagnostics can report which provider won. It does NOT carry the per-reason payload (the unavailable provider id, the ambiguous candidate set, the underlying provider-unavailable reason). That branchable detail lives in the structured `WebError` thrown at execution time, which is the surface callers route on; duplicating it into the status union would give the same fact two homes that can disagree. `searchStatus()` / `fetchStatus()` answer "can this capability run, and if not, in which broad category does it fail" — enough for startup diagnostics and the execution-resolution decision — and the thrown error answers "exactly which provider/ids/reason."
`WebProviderStatus` is an input to selection, not a health system. `tool-web` reads only the aggregated `searchStatus()` / `fetchStatus()`, never each provider's `status()` directly, so selection policy has one owner.
```ts
type WebProviderStatus =
| { readonly available: true }
| { readonly available: false; readonly reason: 'missing-credential' | 'misconfigured' }
type WebCapabilityStatus =
| { readonly available: true; readonly providerId: string }
| { readonly available: false; readonly reason: 'none' | 'configured-missing' | 'configured-unavailable' | 'ambiguous' }
```
Selection must not depend on registration order. Cordis load order, config ordering, and HMR timing are not product semantics.
| Situation | Status / behavior |
|---|---|
| A configured provider id is registered and `status().available === true` | `available: true` for that provider |
| A configured provider id is not registered | `configured-missing`; execution fails with `WEB_PROVIDER_CONFIGURED_MISSING` |
| A configured provider id is registered but unavailable | `configured-unavailable`; execution fails with `WEB_PROVIDER_CONFIGURED_UNAVAILABLE` |
| No provider id is configured and exactly one provider for that kind is registered and available | `available: true` for that single provider |
| No provider id is configured and no provider for that kind is registered | `none`; execution fails with `WEB_PROVIDER_UNAVAILABLE` |
| No provider id is configured and multiple usable providers for that kind are registered | `ambiguous`; execution fails with `WEB_PROVIDER_AMBIGUOUS` rather than choosing by registration order |
| No provider id is configured and providers exist but none are usable | `none`; execution fails with `WEB_PROVIDER_UNAVAILABLE` |
The "single provider auto-selects" rule is for tests, demos, and simple deployments. Product configs should set explicit provider ids:
```yaml
- id: web
name: '@deepseek-ai/dsh-web'
config:
searchProvider: exa
fetchProvider: local-http
- id: web-search-exa
name: '@deepseek-ai/dsh-web-search-exa'
- id: web-search-perplexity
name: '@deepseek-ai/dsh-web-search-perplexity'
- id: web-search-deepseek
name: '@deepseek-ai/dsh-web-search-deepseek'
- id: web-fetch-local
name: '@deepseek-ai/dsh-web-fetch-local'
- id: tool-web
name: '@deepseek-ai/dsh-tool-web'
```
Operational overrides such as environment variables may exist, but they must feed the same explicit selection path. For example, `DSH_WEB_SEARCH_PROVIDER=perplexity` is equivalent to config `searchProvider: perplexity`; it is not a hidden priority chain inside `dsh-tool-web`.
`ctx.web.search()` and `ctx.web.fetch()` resolve the provider at execution time using the same rules as the status query. If the selected capability is unavailable, they throw `WebError` with a structured code such as `WEB_PROVIDER_UNAVAILABLE`, `WEB_PROVIDER_CONFIGURED_MISSING`, `WEB_PROVIDER_CONFIGURED_UNAVAILABLE`, or `WEB_PROVIDER_AMBIGUOUS`. If no provider is explicitly configured and no usable provider exists, the status and execution error are both the generic `none` / `WEB_PROVIDER_UNAVAILABLE` case; the first version should not add a diagnostic summary of every unavailable provider.
## Search request and result schema
The first `web_search` model-facing tool should be small. The only model-facing argument is:
- `query`: required string.
`max_results` is NOT exposed to the model in the first version. It is a `dsh-tool-web`-layer decision: the tool sets the result bound — a default of `8` (aligning with OpenCode's Exa default), as an exported constant mirroring `dsh-tool-fs`'s `READ_LIMIT` / `GREP_LIMIT` — and passes it to the seam as `maxResults` on the `WebSearchRequest`. Keeping it off the model schema means the model just asks a question and the product controls how much context comes back; the field can be promoted to a model-facing argument later without breaking the seam.
`maxResults` flows tool → seam → provider, and the bound is enforced on the way back:
- `dsh-tool-web` owns the value and puts it on `WebSearchRequest.maxResults`.
- `ctx.web` passes the request through to the selected provider unchanged.
- A provider should apply `maxResults` at the request layer when its API supports it (Exa's `numResults`), as a cost/latency optimization.
- `ctx.web` enforces the bound on the result: if a provider returns more than `maxResults` sources — because its API has no result-count control (Perplexity) or ignored the hint — the seam truncates `sources[]` to `maxResults` and sets `WebSearchResult.truncated` to `true` before returning. This makes the bound a single cross-provider guarantee the model-facing layer can rely on, rather than something each provider must remember to honor.
The seam request should not include provider-specific controls such as Perplexity model selection, search recency, domain filters, Exa `livecrawl`, Exa `type`, regional hints, generated-answer budgets, or search depth in the first version. Those fields should be added only when they have provider-neutral semantics that both the tool schema and selected providers can honor honestly.
```ts
interface WebSearchRequest {
readonly query: string
/** Upper bound on returned sources; the seam truncates to it. Omitted = no bound. `dsh-tool-web` always sets it. */
readonly maxResults?: number
}
interface WebSearchResult {
readonly providerId: string
readonly query: string
readonly content?: string
readonly sources: readonly WebSearchSource[]
readonly truncated: boolean
}
interface WebSearchSource {
readonly url: string
readonly title?: string
readonly snippet?: string
readonly publishedAt?: string
}
```
`content` is optional provider-generated answer text, search context, or summary. `sources[]` is the portable citation surface. A source always has a URL; title, snippet, and `publishedAt` are optional because not every provider returns them. `title` should not be required: Perplexity-style citations may provide only URLs, and forcing adapters to invent titles would make the seam lie. `dsh-tool-web` can render `title ?? hostname(url)` for display. `publishedAt` is an optional publication/crawl timestamp as an ISO-8601 string — Exa returns it as `publishedDate` on each result and Perplexity returns a `date` on search results, so it is real provider data, not derived; the seam carries it as a string and leaves date parsing to the consumer.
Exa search should map each entry of the provider's flat `results[]` into a `WebSearchSource`: `url` ← `url`, `title` ← `title`, `snippet` ← the first `highlights[]` entry (an entry with no highlight has no portable snippet and is dropped), `publishedAt` ← `publishedDate`. Exa returns no provider-generated answer, so `content` is omitted. Perplexity search should map `choices[0].message.content` to `content` and prefer the structured top-level `search_results[]` for `sources[]` — `url` ← `url`, `title` ← `title`, `snippet` ← `snippet` (often empty), `publishedAt` ← `date` — falling back to the URL-only `citations[]` array only when `search_results` is absent (those sources carry just a `url`). If a provider returns fewer structured fields than the seam supports, the adapter omits those optional fields.
Full page retrieval remains the job of `web_fetch(url)`. Search snippets are discovery context, not fetched page bodies.
## Fetch request and result schema
The first `web_fetch` implementation should be an anonymous public HTTP(S) fetch provider, likely `local-http`. It should fetch bytes from a concrete URL, apply the basic transport hygiene below (http/https-only, credential rejection, byte/time caps, cross-origin redirect blocking), decode textual content, and return only the minimal model-useful result: final URL, status code, body, and truncation. It should not carry browser cookies, editor credentials, git credentials, internal auth tokens, or implicit access to private services. (Full SSRF / private-network blocking is deferred — see [Deferred work](#deferred-work).)
The first seam request should stay smaller than OpenCode's model-facing tool:
- `url`: required HTTP(S) URL.
- `timeoutMs`: optional positive number capped by the provider.
The seam request deliberately does not include `format`, `prompt`, or provider-specific extraction controls. `format` is a presentation decision over a fetched resource; `prompt` is a higher-level LLM summarization instruction; extraction APIs such as Firecrawl, Exa, Tavily, or Parallel may not expose a concrete HTTP response. If the product later needs provider-backed page extraction, add a separate `web_extract` capability or explicitly widen this RFC before implementation. Do not smuggle extract semantics into `web_fetch` by making every HTTP field optional.
HTTP status is part of the fetched resource state, not automatically a tool failure. A successful network fetch of a `404` or `500` response should return `WebFetchResult` with the status code and a bounded decoded body when the content type is supported. `WebError` is for failures to safely retrieve or represent the resource: invalid or blocked URL, redirect policy violation, timeout, abort, response too large, unsupported content type, provider failure, or network failure.
```ts
interface WebFetchRequest {
readonly url: string
readonly timeoutMs?: number
}
interface WebFetchResult {
readonly providerId: string
readonly url: string
readonly statusCode: number
readonly body: WebFetchBody
readonly truncated: boolean
}
type WebFetchBody =
| { readonly kind: 'html'; readonly content: string }
| { readonly kind: 'text'; readonly content: string }
```
`WebFetchResult.url` is the final URL after allowed redirects. The request URL is already present in `WebFetchRequest`, so the first version should not add separate `requestedUrl` and `finalUrl` fields.
`WebFetchBody` is a CLOSED discriminated union owned by `dsh-web`, not a merge-extensible map. The merge-extensible pattern (`ContentBlockMap`) exists for variants that independent plugins introduce and the seam cannot foresee; body kinds are not that — `dsh-web` declares the kind, the fetch provider decodes it, and `dsh-tool-web` renders it, so a new kind is a coordinated change across three known packages, not a plugin extension. Keeping it closed buys compile-time exhaustiveness: consumers `switch` on `kind` ending in `default: assertNever(body, …)`, so adding a kind breaks compilation at every consumer that must render it (e.g. `tool-web`'s `html`→markdown vs `text` passthrough) until that arm is written. Each arm stays its own object literal even when the fields coincide today, leaving room for arm-specific fields (a future `pdf` body's `pageCount`, a `json` body's parsed value) without reshaping the type. Since the harness is unreleased, extending this closed union later is free (no migration, no compat shim).
The provider owns safe resource retrieval: URL validation, HTTP transport, redirect policy, timeout, abort propagation, byte caps, charset decoding, content-type classification, and binary rejection. `dsh-tool-web` owns presentation: HTML-to-markdown, HTML-to-text, truncation formatting for the model, and future summaries.
The fetch provider must define resource controls before the tool ships:
- Accept only `http:` and `https:` URLs.
- Reject credentials in URLs.
- Enforce maximum URL length, response byte cap, decoded body character cap, timeout, and redirect hop cap.
- Propagate abort signals through network fetches and expensive decoding.
- Automatically follow only same-origin redirects.
- Fail cross-origin redirects with `WEB_REDIRECT_BLOCKED`, requiring a fresh tool call and therefore a fresh provider/permission decision. (Claude Code's WebFetch uses this same model — it does not auto-follow a cross-host redirect; it returns the redirect target to the model for a fresh call.)
- Use an explicit product user agent rather than silently impersonating a browser by default.
SSRF / private-network protection (blocking private, loopback, link-local, multicast, and otherwise non-public destinations, with DNS-resolve-then-validate to defeat rebinding and per-hop re-validation on redirects) is **deferred** — see [Deferred work](#deferred-work). Until it lands, `web_fetch` is an SSRF primitive and must not be enabled in a deployment that can reach sensitive internal network targets.
## Tool consumer behavior
`dsh-tool-web` owns two `ToolDefinition`s: `web_search` and `web_fetch`. It owns model-facing JSON schemas, snake_case argument names, prompt sections, result rendering to `ContentBlock[]`, `presentCall`, and `presentResult`.
`dsh-tool-web` must not enumerate providers or call provider `status()` directly. Its execution path is `ctx.web.search()` / `ctx.web.fetch()`, and any optional startup diagnostics should read only `ctx.web.searchStatus()` / `ctx.web.fetchStatus()`. That keeps provider selection in one layer; otherwise the tool package could decide one provider is usable while execution resolves a different state.
Tool registration in the first version is a minimal stable sync:
1. On plugin startup, read the `dsh-tool-web` `Config` (`search?: boolean`, `fetch?: boolean`, both default `true`) that enables or disables each web tool.
2. If web search is enabled, register `web_search` (its disposer is fiber-scoped via the effect-based registry).
3. If web fetch is enabled, register `web_fetch` (likewise fiber-scoped).
4. Do not dispose either tool merely because `ctx.web.searchStatus()` or `ctx.web.fetchStatus()` is unavailable.
5. Disposing the `tool-web` fiber tears down its registrations automatically.
Provider status changes affect execution results and diagnostics, not whether the model-facing schema exists. If a product wants no web tools at all, it disables `dsh-tool-web` or the individual web tool in config; if it wants web tools but the backend is misconfigured, the model sees a structured tool error at execution time.
Prompt guidance should explain the semantic split: use `web_search` for discovery and current information, then use `web_fetch` when the model needs the content of a specific URL. The prompt and tool result should tell the model to cite relevant URLs with markdown links.
The model-facing output should be text-first because current tool results are `ContentBlock[]`, but the seam outcome should stay structured so UI presentation and future adapters do not have to scrape rendered text.
## Errors
`dsh-web` should define `WebError extends HarnessError` with stable codes. Initial codes should include only states that callers may reasonably branch on:
- `WEB_PROVIDER_UNAVAILABLE`
- `WEB_PROVIDER_CONFIGURED_MISSING`
- `WEB_PROVIDER_CONFIGURED_UNAVAILABLE`
- `WEB_PROVIDER_AMBIGUOUS`
- `WEB_DUPLICATE_PROVIDER`
- `WEB_INVALID_URL`
- `WEB_BLOCKED_URL`
- `WEB_REDIRECT_BLOCKED`
- `WEB_FETCH_TOO_LARGE`
- `WEB_FETCH_TIMEOUT`
- `WEB_ABORTED`
- `WEB_UNSUPPORTED_CONTENT_TYPE`
- `WEB_PROVIDER_ERROR`
`WEB_DUPLICATE_PROVIDER` is thrown synchronously from `registerSearchProvider` / `registerFetchProvider` when an id is already registered for that capability kind (the analogue of `LlmService`'s `DUPLICATE_ADAPTER`); it is a registration-time programming error, not an execution outcome, but shares the `WebError` code space so callers see one taxonomy. `WEB_PROVIDER_ERROR` is the catch-all for a provider's own failure surfaced through the seam, including network/transport failure in `web-fetch-local` (DNS, connection refused, TLS); the first version does not split out a separate `WEB_NETWORK` code, but the provider should set a descriptive message so the model and logs can tell a network failure from a provider API failure.
Tool execution should let these errors flow through `ToolRegistry.execute()`, which already converts `HarnessError` into an error tool result with structured metadata. The model gets a readable error message; hooks, tests, and UI code can route on the stable code.
## Tests
Tests should prove the seam contract without turning this RFC into an implementation checklist.
`dsh-web` tests cover provider registration and disposal, duplicate provider ids, `web/providers-change` emission, rollback when a registration-time `web/providers-change` listener throws, `searchStatus()` and `fetchStatus()` for the selection table above, execution-time provider resolution, `maxResults` truncation of `sources[]` with `truncated` set when a provider over-returns, abort propagation through `WebExecContext.signal`, and structured `WebError` codes.
Search provider tests cover request mapping, response parsing into `content` plus `sources[]`, missing credentials, provider errors, timeout/abort, truncation, and a self-skipping with-key smoke test for each real provider. Perplexity fixtures must include URL-only citations so the optional source fields stay honest.
`dsh-web-fetch-local` tests cover real HTTP behavior using a local test server: valid text and HTML fetches, non-2xx HTTP responses returned as results, byte/decoded-body caps, timeout, abort, invalid URLs, credential-in-URL rejection, cross-origin redirect blocking, unsupported content types, and product user agent. (Private-destination/SSRF blocking tests come with that deferred work.)
`dsh-tool-web` tests execute through the real tool registry. They verify schema registration follows product/app tool enablement rather than provider availability, unavailable or ambiguous providers produce structured execution errors, argument validation, formatting of successful search/fetch results, structured error propagation, and cleanup on disposal.
Integration tests should load the real seam, provider, and tool packages together and execute through `ctx.tools.execute()` rather than calling providers directly. If wiring the tools into an ACP-facing example changes editor-visible transcripts, add or update the relevant snapshot scenario in the same change.
At least one test must drive these packages through their REAL cordis Loader/export path, not a hand-built `ctx.plugin({...})` mount, so a broken export shape is caught (see [docs/postmortem/0001](../../../postmortem/0001-acp-default-export-drops-inject.md) and `packages/AGENTS.md` § plugin-export-shape). The two shapes need different guards: `dsh-web` is a **service** (`export default` the class) and a stray extra export would surface as a missing service; the provider packages and `dsh-tool-web` are **namespace plugins** (named `name`/`inject`/`apply`, NO default), and because each has `inject`, a stray `export default apply` makes `unwrapExports` drop the `inject` and the plugin throws `cannot get property … without inject` the moment it loads — so a Loader smoke that boots tool-web over `ctx.web` catches it (and each provider's registration test mounts it the real way and asserts no default export). Prove the guard bites: add `export default apply` to `tool-web`, watch the smoke go red, revert.
## Migration plan
This is new capability work, so no compatibility migration is required while the harness is unreleased.
Land the work in seam order:
1. Add `packages/web/web` with `ctx.web`, provider registration, provider status, capability status, selection, request/result/error types, and contract tests.
2. Add `packages/web/web-search-exa` with parser/unit tests and a self-skipping real-provider smoke test.
3. Add `packages/web/web-search-perplexity` with parser/unit tests and a self-skipping real-provider smoke test.
4. Add `packages/web/web-search-deepseek` with parser/unit tests and a self-skipping real-provider smoke test.
5. Add `packages/web/web-fetch-local` with local HTTP behavior tests.
6. Add `packages/web/tool-web` with config-driven tool registration, prompt sections, model formatting, presentation, and tool-registry tests.
7. Wire product app/example configs only after package behavior is stable, because tool schemas and prompt sections affect agent behavior and snapshots.
8. Update `docs/architecture.md`, `packages/README.md`, package READMEs, generated Cordis catalogs if new events/services are added, and maintenance scripts.
## Alternatives considered
### Let each provider register its own model-facing tool
This matches the most flexible provider-plugin systems: every provider can expose its full native schema. It is rejected for the harness because it gives provider packages ownership of model-facing names, descriptions, prompt guidance, and result formatting. Multiple search providers would produce duplicate tool names or provider-specific tool names, and the model would learn backend details instead of a stable product capability.
### Put provider dispatch directly in `dsh-tool-web`
This resembles OpenCode's local web search: one stable `websearch` tool dispatches to Exa or Parallel internally. It is acceptable for a small product path but wrong as a harness foundation. The tool package would own provider selection, credentials, request mapping, transport, response parsing, and presentation, making it hard to add Exa and Perplexity without baking their differences into the tool schema.
### Split search and fetch into two seams (`dsh-search`, `dsh-fetch`)
Tempting because the two halves share no request schema and no business logic, so each would map cleanly onto the bash/fs three-package template, and the `Search`/`Fetch` method-pair duplication on `WebService` would disappear. Rejected because the shared machinery — provider-id registry, registration-order-independent selection policy, abort propagation, the `WebError` taxonomy, and the product-facing "how this harness reaches the web" config surface — is real and would otherwise be duplicated across two near-identical seams. One `ctx.web` middle layer gives the product a single thing to inject and configure and gives provider selection one owner. The price is the parallel `searchX`/`fetchX` method pairs, which is accepted deliberately.
### Choose the first registered provider
Rejected. Registration order is not a product policy. It can change with config order, plugin loading, HMR, or refactors. Provider selection must be explicit, or automatic only when exactly one usable provider exists.
### Treat Firecrawl/Exa/Tavily/Parallel extraction as fetch
Rejected for the first version. Those providers often return extracted or summarized content rather than a concrete HTTP response. If the product needs extraction, design `web_extract` or deliberately widen the fetch seam later.
### Mirror Claude Code's `url + prompt` WebFetch shape
Rejected for the seam. `prompt` turns fetch into LLM summarization and couples public-web retrieval to a model provider. The harness seam should fetch and decode deterministically; `dsh-tool-web` can later offer summaries as a presentation mode without making `ctx.web` depend on `ctx.llm`.
## Risks
**The search schema may be too thin.** Exa and Perplexity both expose useful provider-specific controls. The first version should resist adding them until they can be defined provider-neutrally and enforced honestly by both tool registration and provider execution.
**Perplexity citations may be sparse.** A citation may be only a URL. Making `title` and `snippet` optional keeps the seam truthful but means `tool-web` must render useful fallback labels.
**Stable tool registration can defer misconfiguration to execution.** Keeping the tool visible is correct when the product enabled web access, but product apps that expect web search should surface `configured-missing`, `configured-unavailable`, and `ambiguous` loudly during startup diagnostics so users do not discover setup problems only after the model calls the tool.
**Provider state can change after startup.** A tool can be visible in the request assembled at step start and lose its provider before execution. The execution path must resolve again and fail with a structured error.
**Fetch is a network boundary, not just a read-only tool.** `web_fetch` can still reach sensitive network targets or exfiltrate data through URLs. The first version ships only the basic transport hygiene (http/https-only, credential rejection, byte/time caps, cross-origin redirect blocking); SSRF / private-network blocking is deferred (see [Deferred work](#deferred-work)), so until it lands `web_fetch` must not be enabled where it can reach internal targets.
**Large web content can damage context quality.** Providers must enforce byte/character caps and report `truncated`; `tool-web` must format bounded model output with clear continuation or follow-up guidance.
## Deferred work
- SSRF / private-network protection for `web_fetch`: block private, loopback, link-local, multicast, and otherwise non-public destinations so `web_fetch` is not an SSRF primitive. Doing it correctly is more than a URL-string check — it needs DNS-resolve-then-connect-to-the-validated-IP (to defeat DNS rebinding / TOCTOU), per-hop re-validation across redirects, and IPv6 edge handling (private ranges, IPv4-mapped addresses). Neither reference implementation surveyed does IP-level blocking (OpenCode does a prefix check then fetches; Claude Code relies on a centralized hostname blocklist plus a "private URLs will fail" prompt), so there is no implementation to copy and this is the harness's only SSRF defense — it warrants its own focused design/spike. Until it lands, `web_fetch` must only be enabled in deployments that cannot reach sensitive internal targets.
- A `pdf` `WebFetchBody` kind: the `local-http` provider decodes text-extractable PDFs (best-effort, capped, `truncated`) into a `{ kind: 'pdf'; content; pageCount? }` arm, and `tool-web` renders it. This is fetch, not `web_extract` — PDF retrieval is a concrete HTTP 200 plus deterministic local decoding, not provider-side extraction of a non-HTTP resource. Adding it is a coordinated change across `dsh-web` (declare the arm), the provider (decode + narrow "binary rejection" to "reject binary except text-extractable PDF"; scanned/image PDFs needing OCR stay out of scope), and `tool-web` (render). The closed `WebFetchBody` union makes the consumer side fail to compile until the new arm is handled.
- Provider-backed extraction as a separate `web_extract` capability, rather than widening `web_fetch` silently.
- Permission policy integration once the deferred permission system lands.
- Provider-neutral search controls beyond `query` and `maxResults`, once Exa and Perplexity can both honor them honestly.
## Open questions
- Should product app packages treat `configured-missing`, `configured-unavailable`, and `ambiguous` as fatal startup errors when web is explicitly configured, or should `dsh-web` only report status and let apps decide?
- Where should permission policy for public web access live once the deferred permission system lands: a dedicated web permission plugin on `tools/execute`, provider config, or both?

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# RFC: Make `dsh-fs-policy` an event-gate plugin, not a method interface
Status: implemented
## Problem
[The split-fs-seam RFC](../simplification/2026-06-26-fsspec-style-fs-seam.md) put `ctx.fileContext` between the model-facing tools and the `ctx.fs` provider: `dsh-tool-fs` injects `fileContext` and routes every `read`/`write`/`edit` through its methods. That makes `fileContext` **in-path and mandatory**. The tool cannot reach `ctx.fs` without it, the policy layer owns the fs I/O and the read windowing, and a deployment that does not want observed-state policy cannot simply drop the package — `dsh-tool-fs` would fail to resolve `ctx.fileContext`.
This couples three things that should be separable:
1. **What the tool does** — resolve a path, read a window, write/edit a file. This is the tool's job and needs only `ctx.fs`.
2. **The freshness/observation policy** — "edit requires a prior read", "write/edit must be based on the version you read". This is the `dsh-fs-policy` plugin's job.
3. **The recording of observed state** — a side effect that should never block the tool from functioning.
Because the tool calls `fileContext` methods, removing the policy layer is a breaking change rather than a graceful loss of an *add-on*. The policy is load-bearing for the tool to even run, not an opt-in tightening.
## Decision
Invert the control flow. **`dsh-tool-fs` becomes the executor and calls `ctx.fs` directly**; **`dsh-fs-policy` becomes a gate + recorder plugin** that participates through events, never through a method the tool calls and never by registering a `ctx.fileContext` service.
```text
tool dsh-tool-fs executor: resolves, reads windows, writes/edits via ctx.fs;
emits fs policy events; renders results
policy dsh-fs-policy plugin: listens to fs/write-intent +
fs/edit-intent (single-slot waterfall) and fs/observed
(emit) events; adds observed-state + freshness.
provider seam dsh-fs ctx.fs: text IO + ATOMIC mutation primitives whose version
guard is OPTIONAL; owns the fs policy event vocabulary
provider dsh-fs-local local implementation of ctx.fs
```
The model is **additive, not subtractive**: `ctx.fs` on its own is a complete, unconstrained text-storage seam — `read` reads, `write` unconditionally creates-or-overwrites, `edit` unconditionally replaces literal text in the current content. There is no "先读后写", no version check, nothing to remove; the bare provider just does the I/O atomically. `dsh-fs-policy` is a plugin that *adds* constraints on top: observed-state, read-before-edit, and "write/edit must be based on the version you read". So removing `dsh-fs-policy` does not break `dsh-tool-fs` at the service-injection boundary; it removes the policy gate and leaves the bare provider behavior. The intended deployment stance is that a config loading the fs tools also loads `dsh-fs-policy`, so the user-facing behavior and prompt discipline are read-before-write/edit (the `coding-agent` and `acp-agent` demos wire the full stack). The bare-provider mode exists because the tool should not be method-coupled to the policy plugin, not because an unconstrained filesystem is the normal product stance.
`dsh-tool-fs` no longer injects `fileContext`. It injects `fs` and `tools`/`systemPrompt`.
## The policy is enforced by provider CAS, not by `dsh-fs-policy` stat
`dsh-fs-policy` enforces "you must write/edit based on the version you read" **without ever calling `stat` or comparing versions itself**. It supplies the observed version as the CAS basis and lets the provider's mutation critical section detect staleness:
- "Have you read this file?" is the one thing `dsh-fs-policy` decides locally — a `WeakMap` lookup, no I/O. No record ⇒ `FS_NOT_OBSERVED`.
- "Is the version you read still current?" is decided **inside `ctx.fs.editText`/`writeText`**, in the same atomic lock that performs the read-match-rename. `dsh-fs-policy` passes `vObserved` as the expectation; the provider raises `FS_STALE_VERSION` if the file has moved on.
This is deliberate. If `dsh-fs-policy` stat-ed and compared versions in its waterfall handler, there would be a TOCTOU gap between that check and the tool's actual write — the file could change in between, so the check would be a false guarantee that the provider's lock has to back up anyway. Putting the version check in the provider's critical section is both race-free and zero extra `stat`. So `dsh-fs-policy` does **no** filesystem I/O; the "must be based on the latest read" guarantee is *realized* by CAS, and `dsh-fs-policy` only chooses the basis (`vObserved`) and gates on prior observation.
## Provider contract change: the version guard is optional
For the bare provider to be unconstrained, the version guard on its two mutations becomes **optional** — present ⇒ guarded, absent ⇒ unconditional:
```ts ignore-check
// writeText: expected is now optional. The FsWriteIntent union is UNCHANGED.
writeText(target: FsTarget, content: string, expected?: FsWriteIntent, signal?: AbortSignal): Promise<FsWriteOutcome>
// undefined → unconditionally create-or-overwrite (bare default)
// createIfAbsent → create only, reject an existing file (dsh-fs-policy, unobserved) [unchanged]
// replaceIfVersion → overwrite only at the observed version, else FS_STALE_VERSION [unchanged]
// editText: expected becomes optional (was the required { version: FsVersion }).
editText(target: FsTarget, edit: FsEditRequest, expected?: { version: FsVersion }, signal?: AbortSignal): Promise<FsEditOutcome>
// undefined → unconditionally replace literal text in the current content (bare default);
// a missing target still reports FS_STALE_VERSION
// { version } → edit only at that version, else FS_STALE_VERSION (the current behavior)
```
The `FsWriteIntent` union itself does not change — the third "unconditional" state is expressed by *omitting* `expected`, so both mutations share one symmetric shape (`expected?`: omit = no guard, present = guarded). This keeps full backward compatibility for the guarded paths `dsh-fs-policy` uses; only the previously-impossible "no guard" case is new, and it is the bare-provider default. The mutation still runs inside the backend's per-target lock either way, so an unconditional write/edit is still atomic (no torn files); "unconditional" drops the *version* precondition, not the atomicity. `editText` reports a missing target as `FS_STALE_VERSION` on both guarded and unguarded paths, preserving one edit failure code for "the target cannot be edited at this moment".
## Event vocabulary (owned by `dsh-fs`)
The events live in `@deepseek-ai/dsh-fs`, not in `dsh-fs-policy`. This is forced by the decoupling contract: `dsh-tool-fs` is the emitter, so it must reference the event types, and it must keep compiling even though `dsh-fs-policy` no longer provides a method service. `dsh-fs` is the package both `dsh-tool-fs` and `dsh-fs-policy` already depend on, so it is the only home that lets the emitter and the policy listener share a vocabulary without the emitter depending on the policy plugin.
These events carry existing `dsh-fs` vocabulary (`FsTarget`, `FsVersion`, `FsWriteIntent`) plus an opaque actor — not model-facing concepts (no line windows, numbered lines, or rendered footers leak down).
**The two `fs/*` decision events are single-slot decision points, NOT a composable interception chain.** A waterfall listener that does not call `next()` short-circuits the rest of the chain (verified in [vendor/cordis/src/events.ts](../../../../vendor/cordis/src/events.ts) — `waterfall` runs listeners around the final `next` thunk, and a listener that returns without calling `next()` reaches neither later listeners nor the tool's default thunk). `dsh-fs-policy` fully decides the write/edit expectation and does not call `next()`, so it occupies that one decision slot in the default deployment. This is deliberate: "what version basis does this mutation guard against" is a single decision, not an accumulation. The names (`fs/write-intent`, `fs/edit-intent`) say "produce the value", not "authorize", so they do not imply a stackable authorization chain. Genuinely composable interception (permission, audit, sandbox) belongs on the existing `tools/execute` waterfall, which every tool call already flows through — not on this fs version-decision slot.
**The occupant is decided by registration order — first-registered (or `prepend`ed) wins.** cordis dispatches waterfall listeners in registration order (`push`, or `unshift` for `prepend` — [vendor/cordis/src/events.ts](../../../../vendor/cordis/src/events.ts)), and the first non-`next()` decider short-circuits the rest. So the slot is **first-wins**, and `dsh-fs-policy` owning it rests on the default deployment convention: it is the decider registered for these events. The event shape does NOT itself guarantee "an unread edit is rejected" — a plugin that registers a looser `fs/edit-intent` decider BEFORE `dsh-fs-policy` (or with `prepend`) would decide first and bypass the `FS_NOT_OBSERVED` gate. That is the inherent property of a first-wins single slot, stated here so it is not mistaken for an enforced invariant. This RFC does not add a multi-policy composition mechanism; the implementation requirement is that `dsh-tool-fs` dispatches these waterfalls on every write/edit path and that a config wiring the fs tools loads `dsh-fs-policy` as the policy decider.
The actor is typed `object` in `dsh-fs` — a pure opaque carrier the provider seam never reads or narrows. The owner-derivation (`actor.agent?.session`) and the `{ agent?: { session? } }` structural shape stay entirely inside `dsh-fs-policy`, which narrows the `object` actor to that shape in its listeners. `dsh-fs` owns the event names and the fs vocabulary; it does NOT own the policy layer's runtime owner structure.
```ts
import type { FsTarget, FsVersion, FsWriteIntent } from '@deepseek-ai/dsh-fs'
interface Events {
/**
* Single-slot decision: produce the write expectation for the next
* ctx.fs.writeText. The default returns undefined (unconditional create-or-
* overwrite — the bare provider). The policy listener returns createIfAbsent
* (unobserved) or { kind: 'replaceIfVersion', version: vObserved } (observed).
* The listener does NOT call next(): one decision, not a composable chain. @mode waterfall
*/
'fs/write-intent'(target: FsTarget, actor: object | undefined, next: () => FsWriteIntent | undefined | Promise<FsWriteIntent | undefined>): Promise<FsWriteIntent | undefined>
/**
* Single-slot decision: produce the optional version guard for the next
* ctx.fs.editText. The default returns undefined (unconditional edit of the
* current content — the bare provider; no stat). The policy listener returns
* { version: vObserved }, or throws FS_NOT_OBSERVED if the actor is unset or
* has not observed the target. Does NOT call next(): one decision. @mode waterfall
*/
'fs/edit-intent'(target: FsTarget, actor: object | undefined, next: () => { version: FsVersion } | undefined | Promise<{ version: FsVersion } | undefined>): Promise<{ version: FsVersion } | undefined>
/**
* Record that an actor observed a target at a version, after a successful
* read/write/edit. Fire-and-forget (plain emit). Listeners MUST be
* synchronous, side-effect-only recorders (`dsh-fs-policy`'s is a WeakMap
* write); the tool does not guard the emit, so a throwing listener surfaces as
* the tool's isError result. No listener ⇒ nothing recorded.
* @mode emit
*/
'fs/observed'(target: FsTarget, version: FsVersion, actor: object | undefined): void
}
```
The `fs/*` decision events are **unbound waterfalls dispatched by the tool** (like `agent/request`, which the loop dispatches with no `this`), not service-bound waterfalls (like `llm/stream`). The dispatcher is the `dsh-tool-fs` plugin, which is not a service.
## Tool contract (`dsh-tool-fs`)
The tool keeps its model-facing schemas (`read`/`write`/`edit`, byte-for-byte unchanged) and prompt sections. The prompt guidance stays policy-first because a deployment loading the fs tools is expected to also load `dsh-fs-policy`: the model is still told to read before overwriting or editing, and any wording that says the "backend" requires that should be corrected to say the fs-policy plugin requires it. The bare-provider fallback does not change the prompt stance.
`dsh-tool-fs` gains the executor responsibilities relocated from the old `fileContext` method service, including **read rendering** (`read-render.ts`: `buildWindow` + `formatReadOutput`, `READ_MAX_BYTES`, `READ_MAX_LINE_LENGTH`, `FileReadOutcome`/`FileTextLine`, plus `STREAM_MIN_SIZE` in `read.ts`), which is the tool's rendering detail now that the tool owns the read. Those read-rendering types and helpers move into `dsh-tool-fs`; the policy plugin must not remain a type dependency for the tool.
`dsh-tool-fs` is a single root plugin that registers all three tools (`read`/`write`/`edit`), mirroring `dsh-tool-bash`. It injects `fs` (plus `tools`/`systemPrompt`), never `fileContext`. (The original proposal also exposed each tool as a `/read`/`/write`/`/edit` subpath plugin for focused deployments; that was dropped on implementation — no consumer needed a single-tool deployment, and the subpath publishing forced bespoke `tsdown`/`tsconfig`/`files`/workspace-constraint handling no sibling tool package carries. The per-tool registration helpers (`applyReadTool`/`applyWriteTool`/`applyEditTool`) remain internal modules the root plugin composes.)
`stat` budget is minimized by letting the waterfall produce the expectation lazily — the bare default returns `undefined` (no guard) and never stats:
- **read** — one `stat` (type + size routing + version), then `readText`/`streamText`, then `buildWindow`, then an `emit('fs/observed', target, info.version, exec)`. The post-read confirming `stat` from the old `fileContext.read` is dropped; a writer racing between the routing stat and the read can at worst make a *later* guarded edit spuriously `FS_STALE_VERSION` (fail-closed: the model re-reads, never writes against the wrong version, since `editText` re-checks in its lock).
- **write** — `expectation = await ctx.waterfall('fs/write-intent', target, exec, () => undefined)`, then `ctx.fs.writeText(target, content, expectation)`, then an `emit('fs/observed', target, outcome.version, exec)`. **Zero stat in the tool** with or without `dsh-fs-policy`.
- **edit** — `expectation = await ctx.waterfall('fs/edit-intent', target, exec, () => undefined)`, then `ctx.fs.editText(target, edit, expectation)`, then an `emit('fs/observed', target, outcome.version, exec)`. **Zero stat in the tool** in both cases: the bare default is `undefined` (unconditional edit), so the tool never stats to manufacture a basis. If the target is absent, the provider reports `FS_STALE_VERSION` even on the unguarded path.
The tool passes `exec` (the tool-execution context) as the `actor` argument on every dispatch, so `dsh-fs-policy` can derive its observed-state owner. The tool does not know whether the policy plugin is present: it always provides the bare default behavior in the `next` thunk, and `dsh-fs-policy` short-circuits the thunk before it runs in the default deployment.
**`fs/observed` fires AFTER the mutation already succeeded**, via a plain `ctx.emit`. The event contract is intentionally narrow: an `fs/observed` listener MUST be synchronous and side-effect-only — `dsh-fs-policy`'s listener is a `WeakMap.set`, which cannot throw under normal operation and returns no promise. The tool does not guard the emit, so a listener that violates the contract by throwing would surface as the tool's `isError` result ([tools/index.ts](../../../../packages/core/tools/src/index.ts) — `ToolRegistry.execute` catches a tool throw into an error result) — reporting failure for a write/edit that actually happened. That is the price of keeping the event a plain fire-and-forget recorder: cordis `emit` does not await listener promises, so async or fallible audit/telemetry/listener work does not belong on this event. If layered or async observation is ever wanted, that is a new event with its own dispatch story.
## Policy plugin contract (`dsh-fs-policy`)
`dsh-fs-policy` is a plugin, not a service. It does not register `ctx.fileContext`, has no public method surface, and exposes no `read`/`write`/`edit`/`resolve` methods. It attaches three listeners via `ctx.on()` registrations (each returning a disposer for HMR). It keeps the observed-state `WeakMap<owner, Map<targetKey, { version }>>` and the structural owner derivation (narrowing the event's opaque `object` actor to its own `{ agent?: { session? } }` shape), but does not inject `fs` — every handler operates only on its own `WeakMap`, never on `ctx.fs`.
- `fs/write-intent` listener: `prior = getObserved(owner, key)`; return `prior ? { kind: 'replaceIfVersion', version: prior.version } : { kind: 'createIfAbsent' }`. It does NOT call `next()`: it fully owns the single decision slot.
- `fs/edit-intent` listener: `prior = getObserved(owner, key)`; if no `owner` or no `prior`, throw `FS_NOT_OBSERVED`; else return `{ version: prior.version }`. Also does not call `next()`.
- `fs/observed` listener: `record(owner, key, version)`.
An observed-state entry is the **prior-observation record**: a successful `read`, `write`, OR `edit` all emit `fs/observed` and record `{ version }`, so the entry's presence means "this owner has observed this target at this version", not narrowly "has read it". This is what lets a create-then-edit or edit-then-edit sequence work without an intervening re-read: the mutation refreshes the recorded version to its own result, so the next edit's basis is the version it just produced. `FS_NOT_OBSERVED` rejects only an edit with NO prior observation of any kind. The owner is derived structurally from `{ agent?: { session? } }`; disposal drops all state (HMR safety).
`dsh-fs-policy` is now a pure policy/recording plugin with no service surface — it influences the world only through the event seam. That is what removes the method coupling from `dsh-tool-fs`.
## Bare-provider behavior (no `dsh-fs-policy`)
This is not the intended deployment stance — a config loading the fs tools is expected to also load `dsh-fs-policy`. It is the unconstrained provider floor that exists once the tool is no longer coupled to a policy method service. With `dsh-fs-policy` absent, every `fs/*` waterfall falls through to its `undefined` default and `fs/observed` has no listener:
- **read** is identical (it never needed policy; it only emits a now-unheard `fs/observed`).
- **write** unconditionally creates-or-overwrites: `expected` is `undefined`, so `writeText` writes whether or not the file exists and whatever its current version. No read-first requirement, no version check.
- **edit** unconditionally replaces literal text in the file's current content: `expected` is `undefined`, so `editText` matches and rewrites without a version guard or a read-first requirement (`FS_EDIT_NOT_FOUND`/`FS_AMBIGUOUS_EDIT` still apply — those are about the literal match, not freshness). A missing target still reports `FS_STALE_VERSION`, matching the guarded edit path's "cannot edit this target now" code.
Both mutations are still atomic (the backend's per-target lock is unconditional). What is simply *absent*, not lost, is the policy `dsh-fs-policy` would add: observed-state, read-before-edit, and version-guarded write/edit. Loading `dsh-fs-policy` layers those constraints on by having its listeners return guarded `expected` values instead of `undefined`; nothing in the bare provider changes.
## Supersedes
This amends — does not reverse — [the split-fs-seam RFC](../simplification/2026-06-26-fsspec-style-fs-seam.md). The four-layer split, the provider contract, and the freshness *policy* are all kept. What changes is the **coupling between the tool and the policy layer**: a mandatory method service became a plugin-owned event gate, and the fs I/O + read windowing moved from `fileContext` up into `dsh-tool-fs`. The split-fs-seam RFC's description of `dsh-tool-fs` injecting `fileContext` and of `fileContext` owning `read`/`write`/`edit` was updated to match in the same change.
## Acceptance Criteria
- The `dsh-tool-fs` root plugin injects `fs` (+ `tools`/`systemPrompt`), not `fileContext`; it calls `ctx.fs` directly and dispatches the `fs/write-intent`/`fs/edit-intent` waterfalls (passing `exec` as the actor) and the `fs/observed` emit. Read rendering lives in `dsh-tool-fs`. (No subpath plugins — see the Tool contract above.)
- `dsh-fs` declares the three events with `@mode` tags and an opaque `object` actor argument (no agent/session structure leaks into the provider vocabulary); the generated cordis catalog is regenerated.
- `dsh-fs-policy` is a plugin, not a service: it does not register `ctx.fileContext`, has no public `read`/`write`/`edit`/`resolve` methods, and does not inject `fs`; it registers the three listeners, keeps observed-state, and has HMR/disposal coverage (dispose the fiber, assert the gate no longer rewrites).
- **Bare-provider test**: a config WITHOUT `dsh-fs-policy` boots the `dsh-tool-fs` root plugin, and `read`/`write`(create AND overwrite)/`edit` work against the real `dsh-fs-local`; an `edit` of an unread existing file and an overwrite of an existing unread file both succeed (unconditional bare-provider behavior), proving the tool carries no `fileContext` dependency. A bare-provider edit of a missing target reports `FS_STALE_VERSION`. With `dsh-fs-policy` present, the same unread `edit` is rejected `FS_NOT_OBSERVED` and the same unread overwrite uses `createIfAbsent` (rejected on an existing file).
- **Single-slot semantics**: a test registers a second `fs/edit-intent` listener AFTER `dsh-fs-policy` and asserts it is NOT reached (first-wins short-circuit), and documents in a comment that a decider registered before/`prepend`ed would instead win — the slot is first-wins by convention, not an enforced invariant.
- **Fire-and-forget recording**: `fs/observed` is emitted via a plain `ctx.emit` after the mutation succeeds; a listener is contractually synchronous and side-effect-only, so the tool does not guard it.
- `dsh-fs` `writeText`/`editText` make `expected` optional (omit ⇒ unconditional); the `FsWriteIntent` union is unchanged, and `dsh-fs-policy`'s guarded paths (`createIfAbsent`/`replaceIfVersion`/`{ version }`) behave exactly as today. A bare-provider test exercises an unconditional overwrite, an unconditional edit, and a missing-target edit reporting `FS_STALE_VERSION`.
- Freshness is enforced by provider CAS when guarded: an edit after a stale read reports `FS_STALE_VERSION` (regression test); `dsh-fs-policy` performs no `stat`.
- `stat` budget: read = 1, write = 0, edit = 0 — in the tool, with or without `dsh-fs-policy` (the bare default returns `undefined`, never stats). A test asserts neither write nor edit stats in the tool on either path.
- Model-facing schemas stay byte-for-byte unchanged; snapshot transcript goldens are unaffected (or the diff is reviewed and re-recorded with justification).
- Docs/artifacts updated in the same change: `docs/architecture.md`, fs package READMEs, `docs/core-data-structures/filesystem.md`, the split-fs-seam RFC's now-amended description, type-equiv blocks + manifest, cordis catalog, module graph. Gates green: `doc-sync`, `knip`, `test:coverage` (100% per-file).
## Risks
- **Event indirection over a method call.** A waterfall + emit is less direct than `await ctx.fileContext.edit(...)`. The payoff is removing the tool-to-policy method dependency while keeping the default policy plugin; the cost is one more event vocabulary to learn. Mitigated by keeping the three events narrow and documenting the default-thunk semantics on each.
- **Policy events in the storage seam.** `dsh-fs` gains two version-decision events plus a recording event though it is "just storage". This is the price of decoupling (the emitter cannot depend on the policy plugin). The events carry only `dsh-fs` vocabulary plus an opaque `object` actor and no model-facing concepts, so the seam stays free of line-window/observation policy types and of the agent/session owner structure.
- **Single policy occupant, first-wins by convention.** The `fs/write-intent`/`fs/edit-intent` slots hold exactly one decider; the first-registered (or `prepend`ed) listener wins and the rest are short-circuited. `dsh-fs-policy` owning the slot is a deployment convention, not an event-enforced invariant — a second decider registered first would bypass it. This is acceptable because a second fs-version-policy decider is a misconfiguration, not a feature. If a future need for *layered* fs version policy appears, it is a new RFC (a composable value-passing seam), not a silent second listener on these events. Layered permission/audit/sandbox interception already has its home on `tools/execute`.
- **Dropping the post-read confirming stat** makes a follow-up *guarded* edit occasionally fail-closed (`FS_STALE_VERSION` → re-read) under a read/write race. This is a UX nicety lost, never a correctness hole; the provider lock still prevents wrong-version writes.
- **The bare provider does no read-before-write/edit and no version check.** A deployment without `dsh-fs-policy` lets the model overwrite or edit any existing file unconditionally. This is the deliberate meaning of keeping the tool independent of a policy service: the safety disciplines live in the `dsh-fs-policy` plugin. A deployment that omits it is opting into an unconstrained filesystem on purpose; that is not the intended stance for a config that ships the fs tools.

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# RFC: Resolve filesystem paths against the caller's session cwd
Status: implemented
## Problem
The ACP bridge gives every session its own workspace: `session/new` records the editor's project directory as `SessionHeader.cwd`, and `dsh-tool-bash` defaults each bash call's `workdir` to the calling agent's `session.header.cwd` (see [the per-session cwd RFC work in `packages/ui/acp`](../../../../packages/ui/acp) and `resolveWorkdir` in `dsh-tool-bash`). So a bash command in session A runs in A's project, and in session B runs in B's — one server process, N workspaces.
The filesystem tools did NOT honor this. `ctx.fs.resolve(path)` took no caller context, and `dsh-fs-local` resolved every relative path against a single `config.cwd` fixed at plugin load (`process.cwd()`). In the ACP demo that means `write foo.txt` and `bash cat foo.txt` resolve `foo.txt` against **different** directories — the fs tools against the server's launch dir, bash against the session's project dir. The two tools disagree about what "the current directory" is, which is a correctness bug the moment an editor opens any project other than the server's launch dir. It only appeared to work in the snapshot harness because that harness launches the child process in the same temp dir it passes as the session cwd, so the two coincide.
## Decision
Thread the caller's session cwd into path resolution, exactly as `dsh-tool-bash` already does for `workdir`. The **caller** (the tool) supplies the cwd; the provider does not read a session or agent.
- `FileSystem.resolve` widens to `resolve(path: string, opts?: { cwd?: string }): Promise<FsTarget>`. `opts.cwd` is the base a RELATIVE `path` resolves against; an absolute `path` ignores it; omitting `opts.cwd` uses the backend's own default. An options object (not a positional `cwd?`) leaves room for future resolution hints without another signature change.
- `dsh-fs-local.resolve` uses `resolveLocalTarget(opts?.cwd ?? this.config.cwd, path)`. `config.cwd` stays the default for a caller that supplies none (non-ACP / no-session use, and the single-session stdio demo where `process.cwd()` IS the workspace).
- `dsh-tool-fs`'s `read`/`write`/`edit` derive the session cwd through a shared `sessionCwd(exec)` helper (`exec.agent?.session.header.cwd`, mirroring bash's `resolveWorkdir`) and pass it to `resolve`. A non-agent / headerless caller yields `undefined`, so the backend applies its default.
## Why the caller supplies the cwd (not the provider)
The provider seam must not depend on `dsh-agent` / `dsh-session` — it is a text-storage backend that a sandboxed or remote implementation also satisfies, and those have no notion of an "agent session". The tool already receives the `ToolExecution` (`exec`), which carries the agent, so the tool is the right place to project `exec → cwd` and hand the provider a plain string. This is the "explicit > implicit at package seams" convention: the base directory arrives as an explicit argument the provider acts on, not smuggled in by having the provider reach into a session it should not know about. It also matches `dsh-tool-bash` one-to-one, so the two model-facing file surfaces resolve paths identically.
The default lives in ONE place — the provider's `config.cwd`. `sessionCwd` returns `undefined` rather than `process.cwd()` when there is no session, so the tool never manufactures a base the provider would otherwise choose.
## Consequences
- In the ACP demo the fs tools and bash now agree on each session's workspace; an editor can open any project folder and both tool families act on it.
- No change to `FsTarget` identity: `targetKey` is still the realpath of the resolved absolute path, so observed-state keying and symlink identity are unaffected — a correct per-session cwd produces the same key bash targets.
- Backward compatible: every existing `resolve(path)` call (all in tests) keeps working; the new argument is optional.
- The single-session stdio demo is unaffected: it supplies no session cwd (its agent's session has no `cwd`), so resolution falls back to `config.cwd = process.cwd()`, which is the workspace.

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# RFC: Result-time applied-hunk diffs for file mutations
Status: implemented
## Problem
The [tagged render-intent union](2026-07-02-tool-render-intent-union.md) gave `dsh-tool-fs` write/edit a `card:'diff'` at CALL time, derived purely from the tool's args: write ⇒ `{oldText:null, newText:content}` (the whole new file), edit ⇒ `{oldText:old_string, newText:new_string}` (the bare replaced snippet). An editor renders that as an inline diff, but it is a **context-free** diff — the bare `old_string`→`new_string` with no surrounding lines, and a `replace_all` that touched five scattered sites still renders as one snippet pair.
Driving `claude-agent-acp`'s own ACP bridge shows what a full editor diff looks like: after the mutation applies, it emits a SECOND `tool_call_update` whose diff is the **applied hunk with ±3 context lines** (and one hunk per changed site for `replace_all`), reconstructed from the tool's `structuredPatch`. That result-time hunk is what makes Zed show the change *in place* in the file rather than as a floating snippet. Our tools stopped at the call-time snippet; the completed result carried only the plain "updated successfully" text, no diff.
The obstacle is a seam boundary: `presentResult(args, result)` is a **pure function of `args` + the model-facing `result` (`{content, isError}`)** — it runs on live streaming AND on session-log replay, so it must be replay-deterministic and cannot do I/O. It never sees the file's before/after content, and `FsEditOutcome`/`FsWriteOutcome` carried only a replacement count + version, not the text. So there was no way to compute — or even carry — an applied hunk to the presenter.
## Decision
Add a **persisted, tool-private presentation channel** so a tool's `execute` can attach a result-time render payload that survives replay, and use it to carry the applied-hunk diff.
### 1. A `meta` channel on the tool result (core)
`ToolDefinition.execute` may now return either its model-facing `ContentBlock[]` (unchanged, the common case) OR `{ content: ContentBlock[]; meta?: unknown }`:
```ts ignore-check
type ToolExecuteReturn = ContentBlock[] | { content: ContentBlock[]; meta?: unknown }
```
`meta` is an opaque payload the core never interprets — typed `unknown` at every seam (the tool that produced it owns and narrows its shape). It MUST be JSON-serializable: the registry threads it onto the `tool/result` **session event**, and `Session.append` runtime-validates all event data with the existing `isJsonValue` predicate, so a non-serializable `meta` is rejected at the source. On replay the same `meta` is read back and handed to `presentResult` via a widened `ToolResult` (`{ content, isError, meta? }`). Because the payload lives in the event log, the diff reproduces on session reload / snapshot replay **for free** — the event-sourcing guarantee, not a re-computation. Typing `meta` as `unknown` (rather than a shared serializable-value type) keeps the tools core free of a dependency it would otherwise take just to name the type, and the runtime `isJsonValue` gate — not the static type — is what actually enforces serializability.
This is the general shape ("a tool attaches durable result presentation"), not an fs-specific one — any tool can use it.
### 2. The tool computes the hunk; the backend returns before/after (fs)
Per the [capability-seam split](2026-06-13-capability-seams.md), the storage backend returns only **storage facts** and the model-facing tool owns **presentation**:
- `dsh-fs` widens `FsEditOutcome` with `{ before: string; after: string }` and `FsWriteOutcome` with `{ before: string | null; after: string }` (`before: null` ⇒ a create, or an existing-but-undiffable binary/non-UTF-8 file). The local backend already holds both texts at write time; it returns them as raw LF-normalized text, with **no diff/UI concept** entering the seam.
- `dsh-tool-fs` computes the contextual hunk from before/after and attaches it as `meta: { diffs: FileDiff[] }`. A contextual hunk is computed only when a before-version exists — edit always; write on overwrite; a create has no before, matching `claude-agent-acp`'s empty `structuredPatch` on create. But the completed `tool_call_update` is ALWAYS a `diff` card for a successful mutation: an ACP `tool_call_update.content` REPLACES the call's content, so rendering the model-facing result text would clobber the pending diff. So `write`'s result falls back to an args-derived whole-file diff (`oldText: null`) when it has no contextual hunk (a create, or an overwrite whose content is unchanged), and `edit` — which always changes content — always has a hunk. A failed/aborted/policy-rejected mutation applied nothing, so it carries no `meta` and falls through to the generic error rendering (its message must show).
### 3. The bridge renders a `diff` result card
`ToolResultView` gains a `DiffResultView { card:'diff'; title?; diffs: FileDiff[] }`; the bridge's result-side `switch (view.card)` gets a `diff` arm emitting the `{type:'diff'}` `ToolCallContent` blocks (mirroring the call-side arm). An ACP `tool_call_update.content` REPLACES the call's content in an editor, so the result diff **supersedes** the call-time snippet (and keeps the model-facing result text from clobbering it) — the two-update sequence (call snippet, then result diff) matches `claude-agent-acp` exactly.
### The diff algorithm — a third-party runtime dependency over vendoring
Computing hunks-with-context is a solved problem with sharp edge cases (grouping, context coalescing, the trailing-newline marker). Rather than hand-roll it, `dsh-tool-fs` takes a runtime dependency on the npm [`diff`](https://www.npmjs.com/package/diff) package (a `^9.0.0` range, exact-pinned by the lockfile; it ships its own types) and uses its `structuredPatch`. The repo's default is to vendor Cordis-framework source, but that policy is about the *framework*; a leaf tool package taking a small, well-known, self-typed utility dependency is the same shape as `dsh-acp` depending on `@agentclientprotocol/sdk`. Vendoring a diff algorithm would be re-implementing a battle-tested one for no benefit — the [pre-release "foundation over blast radius"](../../../../AGENTS.md) reasoning does not argue for re-deriving standard algorithms. The dependency's output is normalized in one small module (`packages/fs/tool-fs/src/diff.ts`).
## Non-goals
- **Live incremental diff streaming.** The hunk is computed once, after the mutation completes; there is no per-keystroke diff.
- **Diffing a binary/non-UTF-8 overwrite.** `before` is `null` for such a file (it has no text diff basis); the write still succeeds and the result renders a whole-file diff (`oldText: null`) rather than a contextual hunk.
- **Rename/move diffs.** Only content diffs of a single resolved path.
- **Bounding the overwrite diff basis.** An overwrite reads the whole prior file into memory to compute the contextual hunk (on top of the new content already held), so a very large text overwrite allocates both texts for a UI-only diff. A future refinement can bound the pre-read and fall back to a whole-file / no contextual diff above a size threshold; tracked as `TODO(overwrite-diff-bound)` at the read site.
## Related
- Completes the one remaining representation difference named as a non-goal in [Tagged render-intent union](2026-07-02-tool-render-intent-union.md) — that RFC's Non-goals section is updated to record that applied-hunk diffs shipped here.
- Builds on the [filesystem capability seam](2026-06-17-filesystem-capability-seam.md) (the before/after are storage facts the backend returns) and [event-sourced sessions](2026-06-11-event-sourced-sessions.md) (the `meta` payload persists on the `tool/result` event, so replay reproduces the card).
- The `meta` channel is deliberately generic: a future tool (a structured search, a data-table result) can attach its own durable result presentation without another core change.

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# RFC: Tagged render-intent union for tool-call presentation
Status: implemented
## Problem
A tool declares how its calls render in a UI (an editor's tool-call card) through two callbacks, `presentCall`/`presentResult` on `ToolDefinition`, returning `ToolCallPresentation` / `ToolResultPresentation` with an optional `ToolTerminal` sub-shape. These grew incrementally into a **bag of optional fields**: `title`, `kind`, `rawInput`, `content`, `locations`, `terminal` on the call; `title`, `content`, `terminal` on the result; `cwd`/`output`/`exitCode`/`signal` on `ToolTerminal`. The split of responsibility is muddy:
- The call-side and result-side `terminal` fields overlap, and the bridge reconciles a `content` block AND a `terminal` block AND `rawInput` per call, stitching them together with ad-hoc conditionals.
- Which combinations are *valid* is unwritten: a `terminal` call that also sets `content` means "description above the card"; a generic call that sets `terminal` is meaningless but representable. The type permits nonsense.
- There is no way to express the one file-tool affordance an editor most wants — a **diff card** (`{path, oldText, newText}`, which Zed renders as an inline diff / new-file preview). `ToolCallPresentation.content` is the *LLM* `ContentBlock[]` vocabulary (text/image), so a tool literally cannot ask for a diff.
The existing `FIXME(tool-presentation)` in `packages/core/tools/src/index.ts` named the fix: "redesign the type so a tool declares its render INTENT once (e.g. a tagged union over card kinds) rather than a bag of optional fields the bridge stitches together." The rejected RFC [Collapse tool-owned UI presentation](../../rejected/simplification/2026-06-20-generic-tool-rendering.md) deferred it explicitly: rich rendering "should return later as a tagged render-intent union after there are at least two real tools and two real consumers to validate the vocabulary." That bar is now met — two producer families (`dsh-tool-bash`, `dsh-tool-fs`) and two consumers (the ACP bridge live path + the snapshot-golden replay path).
## Decision
Replace the optional-field bag with a **`card`-tagged discriminated union**. A tool declares one render intent per call/result; the bridge switches on the tag.
```ts ignore-check
type FileLocation = { path: string; line?: number }
type FileDiff = { path: string; oldText: string | null; newText: string } // oldText null ⇒ new file
// presentCall → ToolCallView
type ToolCallView = GenericCallView | TerminalCallView | DiffCallView
interface GenericCallView { card: 'generic'; title: string; kind?: ToolCallKind; rawInput?: unknown; content?: ContentBlock[]; locations?: FileLocation[] }
interface TerminalCallView { card: 'terminal'; title: string; description?: string; cwd?: string }
interface DiffCallView { card: 'diff'; title: string; diffs: FileDiff[]; locations?: FileLocation[] }
// presentResult → ToolResultView
type ToolResultView = GenericResultView | TerminalResultView
interface GenericResultView { card: 'generic'; title?: string; content?: ContentBlock[] }
interface TerminalResultView { card: 'terminal'; title?: string; output?: string; exitCode?: number; signal?: string }
```
`card` is **required** on every variant — a real discriminant, not an optional default. The bridge does `switch (view.card) { case 'generic': … case 'terminal': … case 'diff': … default: assertNever(view) }`. The union is **closed** (per the [switch-exhaustiveness convention](../../../../AGENTS.md)): a fourth render intent (a table, a chart) needs new bridge code to render it anyway, so a plugin-added variant that the bridge silently drops would be worse than a compile error. Adding a variant breaks compilation at the bridge switch — exactly the signal we want.
### Why a tagged union beats the field-bag
- **Invalid states become unrepresentable.** A generic card cannot carry terminal output; a terminal card cannot carry a diff. The old bag permitted all of these.
- **The bridge switches instead of stitching.** One arm per card kind, each producing exactly the wire shape that card needs, rather than reconciling five optional fields whose interactions are undocumented.
- **`diff` is a first-class intent.** `dsh-tool-fs` write/edit declare `card:'diff'`; the bridge emits an ACP `{type:'diff', path, oldText, newText}` `ToolCallContent` (already in the SDK's `ToolCallContent` union, previously unused by the bridge). This is the affordance the redesign unlocks.
### Producer mapping
- `dsh-tool-fs` read → `generic` (`kind:'read'`, a follow-along `location`); write → `diff` (`oldText:null`); edit → `diff` (`oldText:old_string || null`, `newText:new_string ?? ''`). This mirrors `claude-agent-acp`'s `toolInfoFromToolUse` Read/Write/Edit arms field-for-field.
- `dsh-tool-bash` foreground → `terminal` call + `terminal` result; `run_in_background` and `bash_output`/`bash_kill` → `generic`.
- `dsh-tool-todo` → `generic`.
### Terminal fallback ownership
`TerminalResultView` carries only `output`/`exitCode`/`signal`. A UI without the terminal capability needs a fenced ` ```console ` text fallback; that derivation moves to the **bridge** (it wraps `output` in a fenced block on the no-capability path), rather than the tool double-encoding it. This keeps the bash tool's result a single structured shape and preserves the existing capability-gated behavior byte-for-byte.
### Purity preserved
`presentCall`/`presentResult` remain pure functions of `args` (+ the result for `presentResult`) — they run on live streaming AND session-log replay, so they must be replay-deterministic. Every view is derived from args alone: write's diff is new-file style (`oldText:null`) because the tool has no old content at call time; edit's diff is `old_string`→`new_string`.
## Relative-path display titles
`claude-agent-acp` relativizes a file card's title path against the session cwd (`toDisplayPath`) — `Read src/foo.ts`, not `/abs/proj/src/foo.ts` — while keeping `locations[]`/`diff.path` **raw** (the editor opens the real path). Our `presentCall` is pure/args-only and cannot see the session cwd, so this relativization happens at the **bridge**, which already threads the session cwd into tool-call rendering (the same cwd it uses to resolve a terminal card's header). The bridge relativizes the title only, by an exact structured replace of the known `locations[0].path`/`diffs[0].path` substring — generic over the file-card kinds, never special-casing tool names.
## Non-goals
- **Live incremental `terminal_output_delta` streaming** and **command classification** — the terminal-rendering RFC's own deferred follow-ups, untouched here.
## Related
- Supersedes the deferral in [Collapse tool-owned UI presentation](../../rejected/simplification/2026-06-20-generic-tool-rendering.md) (rejected — "wait for two real tools and two real consumers, then a tagged render-intent union"). That bar is now met; this is that union.
- Extended by [Result-time applied-hunk diffs](2026-07-02-result-time-applied-hunk-diffs.md), which adds a persisted `meta` channel so write/edit emit a result-time `DiffResultView` — the applied change (a contextual hunk with context lines / one per `replace_all` site, or a whole-file diff for a create) — on top of this union's call-time diff card.
- Folds `ToolTerminal` into the `terminal` views described by [ACP terminal and tool-call rendering](../feature/2026-06-18-acp-terminal-and-tool-rendering.md) (the `_meta` terminal-card convention and capability gate are unchanged; only the harness-side presentation type changes).
- The ACP SDK's `Diff` / `ToolCallContent` types back the new `diff` card.

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# Add direct directory listing to the filesystem seam
## Status
Implemented.
## Context
`@deepseek-ai/dsh-fs` is the provider seam for filesystem access, with local and future non-local backends behind the same `ctx.fs` contract. Before this change it could resolve paths, stat targets, read text, stream text, write text, and edit text. That was enough for model-facing file tools, but not for non-model-facing consumers that need to enumerate directories without importing `node:fs`.
The immediate pressure came from skill loading: reading an individual `SKILL.md` can already go through `ctx.get('fs')`, but discovering which skill roots contain `<name>/SKILL.md` or `<name>.md` still needs directory enumeration. Adding directory listing only in `dsh-skill` would either keep a direct Node dependency there or invent a one-off local helper outside the filesystem provider stack.
This branch deliberately lands the provider capability first and does not add a model-facing `ls`/`list` tool or change skill discovery. The follow-up consumer can validate UX and prompt shape separately, while this PR establishes the backend seam and local implementation.
## Decision
Add `FileSystem.listDir(target, signal?)` to `@deepseek-ai/dsh-fs`.
`listDir` lists one directory level only. It returns direct children in stable name order and includes:
- `name`: the child basename.
- `type`: `file`, `directory`, or `other`.
- `target`: the resolved child `FsTarget`.
- `version`: cheap metadata when available.
- `size`: regular-file size when available.
It never reads file contents. Recursive traversal, globbing, pagination, search, file watching, and model-facing rendering are intentionally out of scope.
The local backend implements this through `readdir({ withFileTypes: true })`, `resolveLocalTarget`, and metadata `stat`/`realpath` probes. The result order is deterministic (`name.localeCompare`) to keep prompt/listing output stable for future consumers and improve prefix-cache reuse.
Broken or disappeared children may be represented as `type: 'other'` without `version`/`size`; they do not abort the whole listing. Permission or backend I/O failures while listing the directory or resolving/probing child metadata fail the whole listing with structured `FsError` codes:
- `FS_NOT_FOUND` for missing targets.
- `FS_NOT_DIRECTORY` for existing non-directory targets.
- `FS_PERMISSION_DENIED` for permission failures.
- `FS_IO_ERROR` for other backend I/O failures.
- `FS_ABORTED` for aborted calls.
## Rejected alternatives
**Add a model-facing list tool now.** Rejected for this PR. The immediate request is the provider seam, and the user explicitly asked not to change skill loading or other upper layers in this branch. A model-facing tool needs prompt/schema/rendering decisions that should be reviewed separately.
**Keep directory enumeration in each consumer.** Rejected. That would bind product packages such as `dsh-skill` to Node/local filesystem behavior and bypass policy/remote/sandboxed backends.
**Make `listDir` recursive or glob-shaped.** Rejected for now. Skill-root discovery only needs direct children, and a simple direct listing is the smallest backend contract future consumers can safely compose.
**Skip children that fail metadata resolution.** Rejected. The API promises resolved child targets, so permission/IO failures while resolving a child are contract failures. Broken or disappeared children are the exception because they can still be represented without claiming a live resolved file.
## Consequences
Every filesystem backend must now implement one additional provider primitive. That is deliberate foundation work while the harness is still unreleased, but it does mean future sandboxed/remote backends need to define equivalent direct-child listing behavior.
The capability remains provider-facing. Until a consumer lands, ACP/model sessions will still need existing tools such as `bash` for directory listing. The absence of a model-facing `listdir` tool is expected, not a wiring failure.

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# RFC: Filesystem tool schemas — model-facing read/write/edit shapes
Status: implemented
## Problem
[The filesystem capability-seam RFC](../architecture/2026-06-17-filesystem-capability-seam.md) defines the filesystem capability seam (`ctx.fs`), the package split (`dsh-fs`, `dsh-fs-local`, `dsh-tool-fs`, plus the `dsh-fs-policy` policy plugin), and the observed-file/stale-version policy for read-before-write/edit checks — which the [split-fs-seam](../simplification/2026-06-26-fsspec-style-fs-seam.md) and [event-gate](../architecture/2026-06-26-file-context-as-event-gate.md) RFCs moved off `ctx.fs` into the `dsh-fs-policy` plugin on the `fs/*` event gate. The remaining decision for the first filesystem tool delivery is the model-facing schema surface: what arguments the model sees for `read`, `write`, and `edit`.
The schema should be small enough to implement in the first `dsh-tool-fs` pass, but stable enough that future local/remote/sandboxed filesystem backends do not require model-facing churn. It should also avoid importing every option from reference systems. Claude Code and OpenCode expose similar core file tools but differ in naming style and extra flags; this RFC chooses the minimal shared surface for the prototype.
## Proposal
`@deepseek-ai/dsh-tool-fs` exposes these three model-facing tools in the first filesystem suite:
| Tool | Our schema | Claude Code | OpenCode | Notes | Part of prototype |
|---|---|---|---|---|---|
| `read` | `read(file_path, offset?, limit?)` | `Read(file_path, offset?, limit?, pages?)` | `read(filePath, offset?, limit?)` | Files only; 1-indexed `offset`; no image/PDF/multimodal support in the first pass. | YES |
| `write` | `write(file_path, content)` | `Write(file_path, content)` | `write(content, filePath)` | Creates or overwrites UTF-8 text. Under the default fs-policy, updates to existing files require a prior observation; new-file creates do not. | YES |
| `edit` | `edit(file_path, old_string, new_string, replace_all?)` | `Edit(file_path, old_string, new_string, replace_all?)` | `edit(filePath, oldString, newString, replaceAll?)` | Literal string replacement; unique match required by default; under the default fs-policy requires a prior observation (any windowed read counts). | YES |
The schema uses snake_case field names (`file_path`, `old_string`, `new_string`, `replace_all`) to align with Claude Code and with existing DeepSeek Harness tool-schema examples. The consumer package translates these model-facing names into `ctx.fs` calls and `fs/*` event dispatches.
## Tool schemas
### `read`
`read` inspects a UTF-8 text file and returns line-numbered content.
Arguments:
- `file_path: string` — required. Path to read, resolved by `ctx.fs`.
- `offset?: number` — optional. 1-based first line to return. Defaults to the first line.
- `limit?: number` — optional. Maximum number of lines to return. Defaults and caps are implementation details of `dsh-tool-fs` / `ctx.fs`.
Non-goals for the first pass:
- No PDF `pages` argument.
- No image or multimodal file reads.
- No directory listing through `read`; if needed, listing becomes a separate future tool.
### `write`
`write` creates or fully replaces a UTF-8 text file.
Arguments:
- `file_path: string` — required. Path to write, resolved by `ctx.fs`.
- `content: string` — required. Full UTF-8 text content to write.
Under the default fs-policy, updating an existing file with `write` requires a prior observation (a read/write/edit) of that file by the same execution context; the `dsh-fs-policy` plugin supplies the observed version as the stale guard on `fs/write-intent`. Creating a new file does not require a prior observation. With the policy plugin absent, `write` is an unconditional bare-provider create-or-overwrite.
The schema does not expose `expected_hash`, `expected_version`, or `create_only` as model-facing parameters. Stale-version checks are driven by backend-produced versions and the policy plugin's observed state, not by asking the model to copy version tokens through the schema.
### `edit`
`edit` updates an existing UTF-8 text file by replacing literal text.
Arguments:
- `file_path: string` — required. Path to edit, resolved by `ctx.fs`.
- `old_string: string` — required. Literal text to replace. Empty strings are invalid in the first pass.
- `new_string: string` — required. Literal replacement text; an empty string deletes the match.
- `replace_all?: boolean` — optional. Defaults to false. When false, `old_string` must identify exactly one match.
`edit` requires a prior observation of the file in the same execution context (any windowed read counts — authorization is version freshness, not a full-view requirement), or a prior write/edit by that context. The `dsh-fs-policy` policy plugin derives the owner and supplies the recorded version as the stale guard; the provider's mutation lock enforces it.
The first pass rejects Codex-style patch grammars and multi-mode edit APIs. It uses one strict literal replacement mode so the model-facing contract stays simple and the backend can own exact-match, duplicate-match, line-ending, and stale-version semantics.
## Result shape
The first implementation returns `ContentBlock[]` through the existing `ToolDefinition.execute()` contract. `ctx.fs` returns structured filesystem results and owns file-state recording/refreshing; `tool-fs` formats those results into the model projection.
Default native projections:
| Tool | Structured `ctx.fs` outcome consumed by `tool-fs` | Default model projection |
|---|---|---|
| `read` | returned lines, returned line count, total line count, target display path, file version, partial-view flag | line-numbered text plus pagination footer |
| `write` | create/update operation, target display path, new file version | concise create/update success text |
| `edit` | replacement count, replace-all flag, target display path, new file version | concise edit success text |
The structured outcome should not restate model arguments such as `file_path`, `old_string`, or `content` unless the backend has resolved them into new information such as `displayPath`, `targetKey`, or a new version. Token-conscious truncation is part of the model projection, not the backend's canonical result.
## Deferred
The following are deliberately out of scope for the first filesystem schema pass:
- Model-facing `expected_hash`, `expected_version`, or `create_only` parameters.
- Directory listing, glob, grep, and search tools.
- Binary-safe read/write operations.
- PDF/image/multimodal `read`.
- Code Mode projection values for filesystem tools.
- A canonical edit diff format.
## Tests
`dsh-tool-fs` schema tests should assert:
- `read` requires `file_path` and accepts optional positive integer `offset` / `limit`.
- `write` requires `file_path` and `content`.
- `edit` requires `file_path`, `old_string`, and `new_string`, accepts optional boolean `replace_all`, rejects empty `old_string`, and defaults `replace_all` to false.
- The registered JSON schemas use the snake_case field names in this RFC.
- The tool descriptions accurately describe that, under the default fs-policy, existing-file `write` and `edit` require a prior observation (any windowed read counts) in the same execution context, while new-file `write` does not.
- The `tool-fs` root plugin registers all three schemas.
Integration tests should execute `read`, `write`, and `edit` through `ctx.tools.execute()` against the real `dsh-fs-local` provider and verify that model arguments are translated into the expected `ctx.fs` calls and `fs/*` dispatches.
## Risks
**The first schema is intentionally smaller than Claude Code's.** Dropping PDF pages, multimodal read, rich grep/list flags, and expected hash fields keeps the first implementation focused, but users may ask for those quickly. They should be added as separate RFCs or focused follow-ups rather than overloaded into the initial schema.
**No explicit model-facing stale guard in v1.** The schema does not ask the model to provide an expected hash/version. That is intentional: stale checks come from backend-produced versions and the `dsh-fs-policy` plugin's observed state, not from fragile model-copied tokens. Filesystem safety failures surface through structured `FsError` codes owned by `dsh-fs`, not through model-supplied version fields.
**Naming becomes public surface.** Once shipped, changing `file_path` to `filePath` or `old_string` to `oldString` would churn prompts, examples, and downstream clients. This RFC chooses snake_case up front and treats it as the stable model-facing contract.

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- A data structure is **core** if it flows through the agent-loop spine — the loop holds, derives, streams, or logs it on every turn regardless of which plugins load (`Message`, `StreamChunk`, `SessionEvent`, the `Agent` handle) — **or** it is the single headline type a plugin author writes against a pipeline (`ToolDefinition`).
- `ToolDefinition` is core (it is what every tool author writes) **even though the loop never holds one** — authoring-importance overrides the strict flows-through-spine rule for this one headline type. But its typing machinery — the `SchemaSpec`/`InferArgs` DSL — is a sub-page detail (you write a `ToolDefinition`; the type-level machinery that types it you do not). That is the spine-vs-seam line made sharp.
- `ToolSchema` is core (it is a field of `GenerateOptions`, the model request that flows through every step) even though it is conceptually part of the tool pipeline — *flows through the spine* wins over *conceptual home* when they conflict.
- The tool-presentation vocabulary (`ToolCallPresentation`, …, carrying a `FIXME(tool-presentation)` redesign marker), the `SessionPersistence` durability seam, and bash vocabulary are sub-pages.
- The tool-presentation vocabulary (`ToolCallView`/`ToolResultView`, …), the `SessionPersistence` durability seam, and bash vocabulary are sub-pages.
`core.md` is a **self-contained spine doc**: it states the exact type definition of each spine structure with minimal prose and links to sub-pages for the per-seam detail. The sub-pages are `llm-streaming.md`, `session.md`, `persistence.md` (split from session along the in-memory-model vs. durability-seam line), `tools.md`, and `bash.md`.

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# Bilingual-pair consistency record (docs/i18n/README.md): the git blob hash of each
# side as of the last confirmed-consistent state. Both languages carry equal authority;
# after editing either side, bring the other along and re-record with:
# pnpm run verify-translation-pairing --write
2026-07-02-bilingual-docs-and-pairing-gate.md: 517a6371eca5d747313c7efdb2756a50257701e4
2026-07-02-bilingual-docs-and-pairing-gate.zh.md: f8f68bf5d4d7e6795318d9dd435a525f20a4f407

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# Bilingual documentation via paired sibling files and a pairing gate
English | [中文](2026-07-02-bilingual-docs-and-pairing-gate.zh.md)
## Context
This repo's README and docs tree are read by people and agents inside and outside the company, in both English and Chinese. Maintaining a second language by hand, with no mechanism, is how translations rot: one side moves on, the other silently lies, and no gate notices. The repo's standing answer to invariants of this kind is to encode them as a mechanical check (see [quality gates](2026-06-11-quality-gates.md) and [doc-sync enforcement](2026-06-11-doc-sync-enforcement.md)), so the bilingual policy ships with one.
## Decision
- **Paired sibling files with equal authority.** A documentation pair is three sibling files: English `foo.md`, Chinese `foo.zh.md`, and a consistency record `foo.i18n.yaml`. Neither language is canonical — a document may be authored and reviewed Chinese-first and translated to English afterwards, or the reverse; what binds the pair is that both sides must say the same thing, and pairs merge whole (both languages plus the record, never one alone). Policy: [docs/i18n/README.md](../../../i18n/README.md); translation rules: [docs/i18n/translation-rules.md](../../../i18n/translation-rules.md); terminology source of truth: [docs/i18n/terminology.md](../../../i18n/terminology.md).
- **A sidecar record of both blob hashes makes consistency checkable.** `foo.i18n.yaml` holds the full git blob hash of each side as of the last confirmed-consistent state. An edit to either side without re-confirming the pair is then mechanically detectable as a pure content comparison — no history lookup — and the hashes are computable for files edited in the same PR, which a commit-hash record is not. Re-recording (`verify-translation-pairing --write`) produces a reviewable yaml diff: confirming consistency is an explicit, visible act in the PR.
- **`verify-translation-pairing` joins `doc-sync`.** The gate ([scripts/verify-translation-pairing.ts](../../../../scripts/verify-translation-pairing.ts)) enforces: required pairs exist, every existing pair is complete (all three files) and consistent (both hashes match, switcher links both ways, structural signatures identical), and excluded (generated or bilingual-by-construction) files stay unpaired. The `required` list in [scripts/translation-pairing.manifest.json](../../../../scripts/translation-pairing.manifest.json) is a ratchet: each merged translation batch adds its files, so coverage only grows.
- **Translation is agent work with human review.** The committed workflow is [.agents/skills/dsh-translate-docs](../../../../.agents/skills/dsh-translate-docs/SKILL.md), following the same pattern as [dsh-code-review](../../../../.agents/skills/dsh-code-review/SKILL.md): the skill carries the workflow and defers to the docs as sources of truth.
## Alternatives considered
- **English as the canonical source with a fingerprint inside the translation** — the design first proposed for this RFC: `.zh.md` files carried an HTML comment recording the English source's blob hash, and translation flowed EN → ZH only. Revised in review: the team wants Chinese-first authoring (write and review a Chinese RFC, then translate to English) with the two languages holding equal authority, which a one-directional canonical model cannot express. The sidecar record covering BOTH sides replaced the in-file one-directional fingerprint; the blob-hash mechanics survived unchanged.
- **Locale directories (`docs/en/` + `docs/zh/`, the Kubernetes/ECharts model)** — rejected: this repo has no docs-site framework to map locales to routes, moving every English file would churn every existing cross-reference, and `verify-md-links`/`verify-doc-refs` would need path-mapping logic instead of working unchanged.
- **A separate translation repo (the PingCAP `docs`/`docs-cn` model)** — rejected: right for a docs product with independent release trains, overkill for a monorepo's own documentation; it also puts the translation outside the reach of this repo's gates.
- **Interleaved bilingual files (single file, both languages)** — rejected: doubles every diff, breaks the one-line-per-paragraph convention's diff ergonomics, and makes partial inconsistency invisible.
- **Commit-hash records (the MDN `l10n.sourceCommit` model)** — rejected in favor of blob hashes: a same-PR edit has no commit hash yet, so the MDN model cannot express "consistent as of the state this PR introduces", and verifying it requires git history instead of file content.
- **Comparing git timestamps of the pair (no record)** — rejected: formatting-only edits would false-positive, and a counterpart committed after an unrelated edit would false-negative; content identity is the only signal that means what the gate claims.
## Industry precedent
Paired sibling files with locale suffixes are the dominant Chinese big-tech convention (ant-design `index.zh-CN.md`/`index.en-US.md`; arco-design `README.zh-CN.md` with a top-of-file switcher; Apache ShardingSphere's 387 `.cn.md`/`.en.md` pairs) — but none of those repos *enforce* pairing or consistency in CI; the convention holds by review alone. Consistency automation exists outside China: MDN's `l10n.sourceCommit` front-matter fingerprint, Vue's Ryu-Cho action (upstream-commit watcher that opens issues/PRs for stale translations), Kubernetes' localization drift scripts, and Microsoft's Azure co-op-translator (source-hash-driven LLM re-translation in CI). This design combines the two: the Chinese-ecosystem file layout with a hash-pair gate, plus a committed agent skill in place of a bot service.
## Consequences
- Editing either side of a paired document obligates the same PR to update the counterpart and re-record the pair — the gate makes the doc-sync rule bilingual, and CI (not reviewer memory) carries the invariant.
- Every pair adds a third file to the tree. The record is machine-written (`--write`), so the cost is directory noise, not maintenance effort; in exchange, "who confirmed these consistent, and when" is answerable from git blame on the yaml.
- When the two sides disagree, no mechanical rule picks a winner — the PR review does. That is the price of equal authority, accepted deliberately: the alternative (a canonical language) forbids Chinese-first authoring.
- Generated docs (`cordis-catalog/`, `tool-catalog/`, `module-graph.md`) are excluded for now; the planned follow-up is to teach their generators to emit Chinese alongside English, at which point they leave the exclusion list.
- Rollout is incremental by design: documents outside `required` are visible backlog (`--list`), not red CI, so pairs land in reviewable batches without a big-bang PR.
- The recorded hashes double as the update tool (`git cat-file -p <hash>` recovers either side's last-confirmed text for a minimal diff-based update), so re-translation of whole files is never forced by the mechanism.

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# 通过配对兄弟文件与配对门禁实现双语文档
[English](2026-07-02-bilingual-docs-and-pairing-gate.md) | 中文
## 背景
本仓库的 README 与 docs 目录树会被公司内外的人和 agent（智能体）以中英两种语言阅读。没有机制、纯靠手工维护第二语言，正是译文腐烂的方式：一侧继续演进，另一侧默默地说谎，而没有门禁会注意到。对这类不变式，本仓库一贯的答案是把它编码成机械检查（见[质量门禁](2026-06-11-quality-gates.md)与 [doc-sync 强制](2026-06-11-doc-sync-enforcement.md)），因此双语政策随附一道门禁一起交付。
## 决策
- **配对兄弟文件，两种语言同权。**一对文档是三个兄弟文件：英文 `foo.md`、中文 `foo.zh.md`，加一份一致性记录 `foo.i18n.yaml`。没有哪种语言是正典——一篇文档可以先用中文撰写和评审、之后再译成英文，反之亦可；约束这对文件的是两侧必须说同样的话，且配对整体合入（两种语言加记录，绝不单独落一侧）。政策见 [docs/i18n/README.md](../../../i18n/README.md)；翻译规则见 [docs/i18n/translation-rules.md](../../../i18n/translation-rules.md)；术语真源见 [docs/i18n/terminology.md](../../../i18n/terminology.md)。
- **旁挂记录两侧 blob hash，使一致性可检查。**`foo.i18n.yaml` 保存两侧文件在上一次确认一致状态下各自的完整 git blob hash。此后改了任一侧而没重新确认配对，都能被机械检测出来——纯内容比较、无需查询历史——而且同一个 PR 里改动的文件也能算出 hash，commit hash 式的记录做不到这一点。重新记录（`verify-translation-pairing --write`）产生一份可评审的 yaml diff：确认一致在 PR 里是一个显式、可见的动作。
- **`verify-translation-pairing` 加入 `doc-sync`。**门禁（[scripts/verify-translation-pairing.ts](../../../../scripts/verify-translation-pairing.ts)）强制执行：required 的配对存在；任何已存在的配对完整（三个文件齐全）且一致（两个 hash 都匹配、切换行双向互链、结构签名一致）；被排除的文件（生成物或本身即双语的）保持不配对。[scripts/translation-pairing.manifest.json](../../../../scripts/translation-pairing.manifest.json) 中的 `required` 清单是一个棘轮：每个合入的翻译批次把自己的文件加进去，覆盖面只增不减。
- **翻译是 agent 的工作，由人评审。**进仓的工作流是 [.agents/skills/dsh-translate-docs](../../../../.agents/skills/dsh-translate-docs/SKILL.md)，与 [dsh-code-review](../../../../.agents/skills/dsh-code-review/SKILL.md) 同一模式：skill 承载工作流，并把真源让给文档。
## 曾考虑的替代方案
- **英文为正典源、指纹放在译文内**——本 RFC 最初提出的设计：`.zh.md` 文件携带一条 HTML 注释记录英文源的 blob hash，翻译只沿 EN → ZH 单向流动。评审中修订：团队需要中文先行的撰写方式（先写、先审中文 RFC，再译英文），两种语言同权，而单向正典模型无法表达这一点。覆盖**两侧**的旁挂记录取代了文件内的单向指纹；blob hash 的机制原样保留。
- **语言目录（`docs/en/` + `docs/zh/`，Kubernetes/ECharts 模式）**——否决：本仓库没有把 locale 映射到路由的文档站框架，挪动每个英文文件会搅动所有既有交叉引用，且 `verify-md-links`/`verify-doc-refs` 将需要路径映射逻辑而不是原样工作。
- **独立翻译仓库（PingCAP `docs`/`docs-cn` 模式）**——否决：适合有独立发布节奏的文档产品，对 monorepo 自己的文档而言过重；还会把译文置于本仓库门禁够不到的地方。
- **中英混排单文件（一个文件、两种语言）**——否决：每个 diff 都翻倍，破坏一段一行约定的 diff 工效，且局部不一致不可见。
- **Commit hash 式记录（MDN `l10n.sourceCommit` 模式）**——否决，改用 blob hash：同一个 PR 内的改动还没有 commit hash，MDN 模式无法表达「与本 PR 引入的状态一致」，且校验它需要 git 历史而非文件内容。
- **比较配对两侧的 git 时间戳（无记录）**——否决：纯格式化的改动会误报，一次无关改动之后提交的另一侧会漏报；只有内容同一性这个信号与门禁的承诺名实相符。
## 业界先例
带语言后缀的配对兄弟文件是中国大厂的主流约定（ant-design 的 `index.zh-CN.md`/`index.en-US.md`；arco-design 的 `README.zh-CN.md` 加顶部切换行；Apache ShardingSphere 的 387 对 `.cn.md`/`.en.md`）——但这些仓库都没有在 CI 里**强制**配对或一致性；约定纯靠评审维系。一致性自动化存在于中国之外：MDN 的 `l10n.sourceCommit` front-matter 指纹、Vue 的 Ryu-Cho action（监视上游 commit、为陈旧译文自动开 issue/PR）、Kubernetes 的本地化漂移脚本、微软 Azure co-op-translator（CI 中由源 hash 驱动的 LLM 重译）。本设计把两者结合：中文生态的文件布局，加 hash 对门禁，再加一个进仓 agent skill（技能）替代 bot 服务。
## 后果
- 修改已配对文档的任一侧，同一个 PR 就有义务更新另一侧并重新记录配对——门禁把 doc-sync 规则双语化，不变式由 CI（而非评审者的记忆）承载。
- 每个配对给目录树多添一个文件。记录由机器写入（`--write`），代价是目录噪音而非维护负担；换来的是「谁在何时确认过这对一致」可以从 yaml 的 git blame 直接回答。
- 两侧说法冲突时，没有机械规则裁决谁赢——由 PR 评审裁决。这是同权的代价，是有意接受的：另一个选项（正典语言）禁止中文先行撰写。
- 生成文档（`cordis-catalog/`、`tool-catalog/`、`module-graph.md`）暂被排除；计划中的后续工作是让它们的生成器在输出英文的同时输出中文，届时移出排除清单。
- 推进天然是渐进的：`required` 之外的文档是可见的 backlog（`--list`），不是红的 CI，因此配对按可评审的批次落地，无需一个巨型 PR。
- 记录的 hash 兼作更新工具（`git cat-file -p <hash>` 能还原任一侧上次确认的文本，用于基于 diff 的最小更新），所以这套机制从不强迫整篇重译。

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# RFC: Generated tool-schema catalog (boot-and-harvest)
Status: implemented (accepted 2026-07-02)
## Context
A reader — a plugin author, a prompt engineer, someone auditing what the agent can do — has no single place that lists the model-facing tools the harness ships. The `name` / `description` / JSON-Schema `parameters` a tool contributes are what the model actually receives (via `ctx.systemPrompt.tools()` off `ctx.tools.schemas()`), but they are scattered across each `defineTool` call in each `packages/*/tool-*` package, buried in string concatenation and runtime spreads. The [cordis events & services catalog](../../../cordis-catalog/events-and-services.md) ([its RFC](2026-06-20-generated-cordis-catalog.md)) documents the *wiring* a plugin works against and the [core-data-structures catalog](../../../core-data-structures/core.md) documents the *vocabulary* those signatures move — but neither documents the *tools* the agent is offered. This RFC adds that third reference surface, `docs/tool-catalog/tools.md`, and a freshness gate so it cannot drift.
## Decision
Generate the catalog by **booting each tool plugin and reading its registered schemas**, not by parsing source. `scripts/gen-tool-catalog.ts` mounts each shipped tool package on a fresh cordis `Context` (with `SystemPrompt` + `ToolRegistry` and the injected seams the plugin's `apply` reads), calls `ctx.tools.schemas()` — exactly the `ToolSchema[]` the model is sent — disposes the context, and renders one `## <package>` section per package with a ` ```json ` `parameters` block per tool. It mirrors the `gen-cordis-catalog` / `gen-module-graph` CLI shape: default `--write` regenerates, `--check` fails if the committed copy is stale, output is deterministic (manifest-ordered, tools sorted by name). `verify-tool-catalog` (the `--check`) runs inside `doc-sync`, so the freshness gate fires in the same lefthook pre-push and CI paths as every other doc gate.
### Why boot, not parse (the crux)
The cordis catalog is a pure TypeScript-AST pass because every event/service name is a string literal that round-trips to a static declaration — the AST is the whole truth. **Tool schemas are not statically knowable**, so the same technique would produce a doc that lies:
- `tool-todo` writes `enum: [...STATUSES]` — a spread of a runtime `const`. The AST sees the spread expression, not `["pending","in_progress","completed"]`.
- Every description is built by string **concatenation** (`'…' + '…'`). The AST sees concatenation nodes, not the final prose the model reads.
- `tool-subagent`'s tool name is `config.toolName ?? 'subagent'` — chosen at load, not a literal.
- An MCP plugin can register **raw JSON Schema** directly via `ctx.tools.register()` without `defineTool` at all, so enumerating `defineTool(` call sites structurally under-counts.
The only faithful source of truth is the schema the registry actually holds after the plugin loads. Booting is the [unit-test discipline](../../../../AGENTS.md) "verify the world, not a synthetic stand-in" applied to a doc generator: read the shipped artifact, not a re-derivation of it.
### Restoring "nothing silently omitted"
Booting has a cost the AST pass did not: there is no source declaration set to enumerate, so a new tool package could simply be forgotten. A **completeness guard** restores the guarantee — `assertManifestComplete` globs every `tool-*` package under `packages/` and hard-errors if any is absent from the generator's boot manifest. A new tool package fails the generator, and therefore `doc-sync`, until it is registered. This is the same structural property the cordis generator gets for free from enumerating source, re-created for a boot-based generator.
### A hand-maintained boot manifest is the irreducible policy
The boot manifest (`TOOL_PACKAGES`) is a hand-written list — in tension with the proposed [Discover package inventories instead of maintaining static lists](../../proposed/process/2026-06-20-discover-package-inventory.md). The tension is deliberate and resolved as follows: the *inventory* is discovered (the glob guard means no one maintains "the list of tool packages" — the filesystem is the source of truth, and drift fails the gate), but the *boot recipe* per package — which seams to plug (`bash-local` for `ctx.bash`, `subagent` + `subagent-mock` for `ctx.subagents`) and with what config (`{ provider: 'mock' }`) — is genuine policy that no layout fact encodes. Per that RFC's own "what we give up" ("stay boring: read manifests, filter on explicit fields, print the resolved list, and fail loud"), a recipe closure is the boring, explicit form; inferring seam wiring from injects would be the "too clever" path it warns against. So: discovered inventory, hand-written recipe, gate on completeness.
### Scope
Shipped product tool PACKAGES under `packages/*/tool-*`, each booted with its default config: `dsh-tool-bash` (`bash`, `bash_output`, `bash_kill`), `dsh-tool-todo` (`todo_write`), `dsh-tool-subagent` (`subagent`). The `examples/` demo tools (`echo`) are excluded, matching the cordis catalog's packages-only scope — a demo tool is not part of the product surface a reader is cataloguing.
The unit is the PACKAGE, not the deployed tool instance. A package's registered tool name can be a load-time config — `tool-subagent`'s `toolName` — so the same package surfaces as `subagent` (spawn backend) AND `subagent_fork` (fork backend) in the shipped `coding-agent` / `acp-agent` configs, with an identical schema. The generator boots each package once at its default and records such shipped aliases in a per-package note, rather than enumerating every deployment permutation. Cataloguing at the package level keeps the source of truth the package (what a plugin author reads) and avoids leaking example-app `cordis.yml` config into a packages-scoped generator; the note keeps the doc honest about the names a reader will actually see the model receive. The design deliberately does not attempt to catalog "every configured tool instance across every leaf config" — that is a deployment inventory, a different (and unbounded) surface.
### A plain `json` fence
Schema blocks use ` ```json `, not a bespoke `ts`-family fence. `doc-typecheck` only extracts `ts*` fences, so a JSON block is invisible to it — no `BlockKind` wiring is needed (unlike the cordis catalog's `ts cordis-catalog` fence, which had to be allowlisted so a bare signature fragment isn't compiled).
## Consequences
- The catalog cannot drift: a tool schema change the committed file doesn't reflect fails `verify-tool-catalog` in the pre-push hook and CI. A new `tool-*` package not added to the manifest fails the completeness guard outright.
- Tool description prose has a single home — the `defineTool` `description` at the source — and the generated entry is only as good as it, the same forcing function the cordis catalog applies to event JSDoc.
- The generator imports and executes workspace packages (the first repo script to do so; the others only read text). It runs under `tsx` via the root `tsconfig` `paths` map, the same unbuilt-source path the demos and tests use, so it needs no build step.
- A new capability seam behind a future tool means a new manifest recipe entry (which seams to mount). This is the deliberate hand-written cost called out above; it changes only when a tool package is added.

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# RFC: Split the filesystem seam — provider text mutations plus the `dsh-fs-policy` plugin
Status: implemented
## Problem
The filesystem capability from [filesystem-capability-seam](../../implemented/architecture/2026-06-17-filesystem-capability-seam.md) currently makes one abstract `FileSystem` service own two different jobs:
1. **Provider operations** — resolving targets, stat/version metadata, text reads/streams, atomic writes, and guarded literal edits.
2. **Agent-facing policy** — line windows, literal edit semantics, and read-before-write/edit observed-state.
That makes every future backend reimplement model-facing read semantics and observation policy. `readPage` returns numbered lines and view metadata; the base service stores per-owner file state and distinguishes `full` from `partial` reads. Those are useful policies, but they are not filesystem-provider primitives. Literal text mutation is different: version guard, literal match, ambiguity detection, and atomic rewrite must stay together inside the provider mutation boundary, but the current `applyEdit` name and surrounding seam tie that provider operation to the old read-before-edit policy shape.
This also creates a real UX dead-end: a windowed read records `view: partial`, and partial views cannot authorize `edit`. A model that reads lines 100-150 of a large file therefore cannot edit line 120 unless it first gets a `full` read, which may be impossible for a file past the read cap. Literal edit only needs freshness: the bytes being matched must still be from the version the model read.
The old RFC already deferred a separate `@deepseek-ai/dsh-fs-policy` package. This RFC builds that layer and keeps `ctx.fs` close to fsspec-style storage primitives (`info`/`cat`/`open`), without turning it into full fsspec.
## Decision
Split the stack into four layers:
```text
tool dsh-tool-fs model-facing schemas + read windowing + text rendering; the EXECUTOR (reads/writes/edits via ctx.fs, dispatches the fs/* events)
policy dsh-fs-policy observed-state + read-before-edit + write/edit freshness, contributed through the fs/* event gate (no service)
provider seam dsh-fs ctx.fs: text IO + atomic mutation primitives (optional version guard)
provider dsh-fs-local local implementation of ctx.fs
```
`dsh-tool-fs` keeps the same model-facing `read`/`write`/`edit` schemas. It is the executor: it injects `fs` (not a policy service) and reaches `ctx.fs` directly, owns read windowing, and dispatches the `fs/*` events so `dsh-fs-policy` can gate and record.
This RFC decided the four-layer split, the provider contract, and the freshness policy. The tool↔policy COUPLING was then refined by [the event-gate RFC](../architecture/2026-06-26-file-context-as-event-gate.md): `dsh-fs-policy` is a gate PLUGIN that participates through the `fs/*` events rather than a `ctx.fileContext` method service, so the tool is not method-coupled to it and read windowing + the fs I/O live in `dsh-tool-fs`. This document describes that landed event-gate shape; the provider's version guard is optional (omit = unconditional bare provider).
## Provider Contract
`@deepseek-ai/dsh-fs` shrinks to provider text IO plus guarded text mutation:
```ts ignore-check
abstract resolve(path: string): Promise<FsTarget>
abstract stat(target: FsTarget, signal?: AbortSignal): Promise<FsInfo | undefined>
abstract readText(target: FsTarget, signal?: AbortSignal): Promise<string>
abstract streamText(target: FsTarget, signal?: AbortSignal): Promise<AsyncIterable<string>>
abstract writeText(target: FsTarget, content: string, expected: FsWriteIntent, signal?: AbortSignal): Promise<FsWriteOutcome>
abstract editText(target: FsTarget, edit: FsEditRequest, expected: { version: FsVersion }, signal?: AbortSignal): Promise<FsEditOutcome>
interface FsInfo {
version: FsVersion
type: 'file' | 'directory' | 'other'
size?: number
}
type FsWriteIntent =
| { kind: 'createIfAbsent' }
| { kind: 'replaceIfVersion'; version: FsVersion }
```
`stat` returns metadata, not content. `version` is the freshness token; `type` lets the executor reject directories/special files before reading; `size` lets the `read` tool choose `readText` vs `streamText` without probing by failure. `undefined` means absent.
`readText` reads the whole regular text file. `streamText` streams the same text semantics for large files. Both provider primitives own regular-file checks, UTF-8 decoding, binary/NUL rejection, and `FS_NOT_TEXT`; the policy layer never handles raw bytes or reimplements cross-chunk decoding. `readText` is the small-file/direct whole-file primitive, while large model-facing reads use `streamText`.
`writeText` is atomic temp-file + rename with an explicit write expectation. `createIfAbsent` creates a missing target and rejects an existing target with `FS_NOT_OBSERVED`; it is the path used when the owner has no prior read. `replaceIfVersion` replaces only when the target exists at the observed version; a missing target or version mismatch throws `FS_STALE_VERSION`.
`editText` is a provider-level guarded text mutation. When guarded it first verifies the target still exists at `expected.version`, then reads the current text, applies literal replacement, and writes atomically. The stale check must happen before literal matching so an edit based on an old read reports `FS_STALE_VERSION`, not `FS_EDIT_NOT_FOUND` or `FS_AMBIGUOUS_EDIT` from matching against newer content. Keeping this primitive on the provider seam preserves backend-local locking and lets a future remote backend implement native compare-and-edit without forcing the policy layer to pull the whole file through it.
This is a *text-storage* seam, deliberately half a level above byte-level fsspec (`cat`/`open` hand back raw bytes). UTF-8 decoding, binary/NUL rejection, guarded full-file writes, and guarded literal text edits live in the provider so the policy layer never touches raw bytes, reimplements cross-chunk decoding, or separates stale checks from the mutation critical section. Model-facing concepts still stay out of the provider: no line windows, numbered lines, rendered footers, or observed-state store leak down.
Deleted from `dsh-fs`: `readPage`, `FsExpectation`, `FsView`, `FsStateSource`, `FsReadRequest`, `FsTextLine`, line/window constants, `formatReadBody`, and the observed-state `WeakMap`. `applyEdit` is replaced by the narrower provider primitive `editText`, whose contract is version-guarded literal text mutation rather than policy-layer read authorization. The `FS_PARTIAL_OBSERVATION` code also leaves the `FsErrorCode` taxonomy: freshness authorization has no partial/full distinction, so nothing can raise it. `FsTargetKey` and `FsVersion` become branded opaque ids under the existing [branded-ids RFC](../../implemented/architecture/2026-06-20-branded-ids.md).
## Policy Contract
`@deepseek-ai/dsh-fs-policy` is a plugin, not a service: it registers no `ctx.*` key and injects nothing. It owns the write/edit freshness policy and observed-state that do not belong on the `FileSystem` provider base class (where a sandboxed/remote backend would otherwise inherit model-facing observation policy it has no business carrying). It contributes that policy through the `fs/*` event gate the executor dispatches. (This RFC originally proposed a concrete `ctx.fileContext` service with `read`/`write`/`edit` methods; [the event-gate RFC](../architecture/2026-06-26-file-context-as-event-gate.md) refined it into the plugin described here so the tool is never method-coupled to the policy.)
Observed state lives here as `WeakMap<owner, Map<targetKey, FsVersion>>`. An entry exists iff the owner has read, written, OR edited that target (every success emits `fs/observed`), so its presence *is* the prior-observation record — there is no separate `hasRead` flag. The owner is derived structurally from the opaque event actor (`{ agent?: { session? } }`), a shape that lives in `dsh-fs-policy`, not `dsh-fs`.
The plugin decides three `fs/*` events:
- `fs/write-intent` — no prior observation ⇒ `{ kind: 'createIfAbsent' }` (only new files can be created blindly); a prior observation ⇒ `{ kind: 'replaceIfVersion', version: vObserved }` (existing files replaced only if unchanged since the observation). Single-slot decision; does not call `next()`.
- `fs/edit-intent` — requires a prior observation by the owner (else `FS_NOT_OBSERVED`); returns `{ version: vObserved }` as the CAS basis. It does not implement literal replacement — it authorizes and supplies the version, and the provider's mutation critical section applies the guard, so concurrent edits based on the same observed version remain one-wins/one-stale.
- `fs/observed` — records `{ version }` for this owner+target after a successful read/write/edit. Synchronous, side-effect-only `WeakMap.set`.
The plugin does NO filesystem I/O: "have you observed this file?" is a `WeakMap` lookup, and "is the version you read still current?" is decided inside `ctx.fs.editText`/`writeText` in the same atomic lock that performs the mutation — the plugin only supplies `vObserved` as the basis.
## Tool Contract
`dsh-tool-fs` keeps the same schemas and prompt surface. `read` still exposes `file_path`, `offset`, and `limit`; `write` and `edit` are unchanged. It is the executor: it validates model args, reads/writes/edits through `ctx.fs` directly, owns line windowing and result rendering (`N: text`, footer, `<path>/<content>` envelope), and dispatches the `fs/*` events.
Each mutation dispatches its intent waterfall with an `undefined` bare-provider default, then calls `ctx.fs`, then emits `fs/observed`: e.g. `write` does `ctx.waterfall('fs/write-intent', target, exec, () => undefined)` → `ctx.fs.writeText(target, content, intent)` → `ctx.emit('fs/observed', …)`. A `read` stats once, reads/streams, builds the window, and emits `fs/observed`. Passing `exec` as the actor lets `dsh-fs-policy` derive the owner without the tool reaching into the policy.
Because the policy is contributed through events with an `undefined` default, `dsh-tool-fs` is not method-coupled to `dsh-fs-policy`: with the plugin absent, every intent waterfall falls through to `undefined` (unconditional bare-provider write/edit) and `fs/observed` has no listener. Loading the plugin back layers the read-before-write/edit policy on.
## Concurrency Boundary
In-process updates are safe: the local backend keeps the existing per-target mutation lock, so version-check-then-rename is serialized and a losing update sees `FS_STALE_VERSION`.
In-process creates are guarded by the same per-target mutation lock: two callers racing with `createIfAbsent` serialize, one creates, and the next sees the target exists and receives `FS_NOT_OBSERVED`. Cross-process creates are best-effort only; a local stat-then-rename guard cannot make portable create-exclusive guarantees across all future backends.
Cross-process writes are best-effort freshness plus atomic replacement: `mtime:size` usually catches editor saves, but same-tick same-size writes can miss; atomic temp+rename prevents torn files but not every lost update.
## Supersedes
This RFC reverses two decisions from [filesystem-capability-seam](../../implemented/architecture/2026-06-17-filesystem-capability-seam.md) and narrows a third:
- Read-before-write/edit policy moves out of `ctx.fs` and into the `dsh-fs-policy` plugin (on the `fs/*` event gate).
- Text reads no longer return backend-numbered line records or `full`/`partial` views; authorization is based on version freshness, so a windowed read can authorize edit when the file is unchanged.
- Literal edit no longer sits behind the old `applyEdit` API that mixed backend mutation with seam-owned observation policy. It remains a provider primitive as `editText`, because version guard + literal match + atomic rewrite must stay inside the provider's mutation critical section.
It keeps the interface/implementation/consumer discipline, consumer-never-imports-backend rule, backend-defined target/version/display metadata, atomic local writes, and the shared `FsError` taxonomy.
## Acceptance Criteria
- `dsh-fs` exposes exactly `resolve`/`stat`/`readText`/`streamText`/`writeText`/`editText`; `stat` returns `FsInfo | undefined`; `writeText` uses `FsWriteIntent` (`createIfAbsent` or `replaceIfVersion`); removed types/primitives are gone, and the old `applyEdit` API is replaced by `editText`.
- `dsh-fs-policy` adds the observed-state + `read`/`write`/`edit` freshness policy and has HMR/disposal coverage. (It does so as a gate PLUGIN on the `fs/*` events with no `ctx.fileContext` service, per [the event-gate RFC](../architecture/2026-06-26-file-context-as-event-gate.md) — the original service form this RFC proposed was reworked.)
- `dsh-tool-fs` reaches the policy decisions and model-facing schemas stay byte-for-byte unchanged; the observation contract (a read records observed-state; a direct `ctx.fs` read does not) is documented and tested. (The tool injects `fs` and dispatches the `fs/*` events rather than injecting a `fileContext` service, per the event-gate RFC.)
- Windowed read authorizing edit is shown to fail on the pre-refit code and pass after the refit. Existing version-CAS behavior is preserved with a regression test; it is not claimed as a pre-refit failure. An edit based on a stale read must report `FS_STALE_VERSION` before attempting literal matching.
- `dsh-fs-local` carries no line, view, or `formatReadBody` logic; it does carry provider-level `editText` logic.
- Docs and generated artifacts are updated: `docs/architecture.md`, `packages/README.md`, fs package READMEs, `docs/core-data-structures/filesystem.md`, affected `type-equiv` blocks and `scripts/type-equiv.manifest.json`, Cordis catalog, module graph, and doc references.
- Gates stay green: normal `doc-sync`, `pnpm run knip`, and `pnpm run test:coverage` with 100% per-file coverage.
## Later extension
The seam was later extended with direct directory listing by [Add direct directory listing to the filesystem seam](../architecture/2026-07-03-filesystem-directory-listing-seam.md). That follow-up is tracked separately so this RFC's acceptance criteria continue to describe the fsspec-style refit that originally shipped.
## Risks
- Adds a fourth fs package and a new service. This is intentional: it is the previously deferred policy layer, not a second abstract backend seam.
- Direct `ctx.fs` use bypasses the policy: a direct `ctx.fs.readText` emits no `fs/observed`, so under the default policy a later `edit` rejects with `FS_NOT_OBSERVED` until the file is read through the `read` tool. The failure is explicit and documented.
- Large-file line windowing moves from the backend to the `read` tool in `dsh-tool-fs`; text decoding and binary rejection stay in `ctx.fs.streamText`, so this is relocation of windowing only, not a second text-IO implementation.
- Keeping `editText` in the provider seam means every backend must implement the literal replacement contract. This is intentional: the operation is not pure storage, but stale guard + literal match + atomic rewrite is the unit that must stay together for correct error attribution and concurrency behavior. The contract should stay narrow and text-only so future backends can implement it natively or by whole-file rewrite.
- Freshness permits full-file `write` after a windowed read. That is weaker than the old view check, but avoids making large files impossible to edit; prompt guidance should still discourage blind full replaces.